Application of Solar Technology to Today's

Energy Needs—Vol. I

June 1978

NTIS order #PB-283770
Library of Congress Catalog Card Number 78-600060

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402, Stock No. 052-003-00539-5
FOREWORD

This report reviews a range of solar energy systems designed to

produce thermal and electrical energy directly from sunlight with

units small enough to be located on or near the buildings they are

designed to serve. It examines the state-of-the-art of the technology,

identifies the circumstances under which such systems could be

economicalIy attractive, and discusses the problems encountered in

integrating these devices into existing energy generation and

delivery systems. The study also assesses the impact that widespread use of decentralized solar energy equipment could have on

the United States — its energy supplies, its ability to achieve foreign

policy objectives, its physical environment, its levels and patterns

of employment, and the functioning of society as a whole. It is apparent from the study that development of a large market for such

equipment would have a profound impact on the way an industrial

society evolves.

The analysis conducted for this report found that with aggressive Federal support, there are realistic circumstances in which

small-scale energy systems could compete favorably with conventional energy sources in many residential, commercial, and industrial applications by the end of the next decade. Given the

limited number of choices available for meeting our future energy

needs, the options made available by this technology deserv e

serious consideration

RUSSELL

Directo r

Off ice of

W. PETERSON

Technology Assessment

.

///
OTA Solar

Advisory Panel

Jerry Grey, Chairman

Private Consultant

William W. Caudill

Caudill, Rowlett & Scott

John J. Gunther

United Conference of Mayors

Klaus P. Heiss

ECON, Inc.

Morton Hoppenfeld

University of New Mexico

Charles Luttman

The Ralph M. Parsons Company

James MacKenzie

Massachusetts Audubon Society

Paul Maycock

Texas Instruments’

Marjorie Meinei

University of Arizona

Larry T. Papay

Southern California Edison Co.

Paul Rappaport

RCA-David Sarnoff Research Center**

Floyd E. Smith

International Association of

Machinists

Ephraim M. Sparrow

University of Minnesota

OTA Energy

Advisory

Committee

Milton Katz, Chairman

Director, International Legal Studies, Harvard Law School

Thomas C. Ayers George E. Mueller

President and Chairman of the Board President and Chairman of the Board

Commonwealth Edison Company System Development Corporation

Kenneth E. Boulding

Professor of Economics

Institute of Behavioral Science

University of Colorado

Eugene G. Fubini

Fubini Consultants, Ltd.

Levi (J.M.) Leathers

Executive Vice President

Dow Chemical USA

Wassily Leontief

Department of Economics

New York University

Gerard Piel

Publisher, Scientific American

John F. Redmond, Retired

Shell Oil Company

John C. Sawhill

President

New York University

Chauncey Starr

EIectric Power Research

Institute

*Resigned after accepting posltlon with U S Department of Energy.

* * Resigned after accepting position as Director of the Solar Energy Research I nstltute

iv
OTA Solar Energy

Project Staff

Lionel S. Johns, Energy Program Manager

Henry Kelly, Project Leader

David Claridge

OTA Energy Staff

Richard Rowberg

Lynda Brothers

Marvin Ott

Dorothy Richroath

Linda Parker

Lisa Jacobson

Joanne Seder

Radmilia L. Bartok

Rosaleen Sutton

TechnicaI Assistance

Oak Ridge National Laboratories

Sandia Laboratories

Lawrence Livermore Laboratory

Department of Energy

Division of Solar Energy

Contractors

American Institute of Architects

Research Corporation

Environmental Law Institute

Thermo Electron Corporation

OTA

Publications

Staff

John Furber John Bell

Consultants

Timothy Adams

Linda Ashworth

Richard Bourbon

Allen Brailey

Jack Burby

Peter Ceperley

Thomas Erwin

Crayson Heffner

Sam iker

Ann Cline Kelly

Renal Larson

Robert Morse

Corbyn Rooks

Edward Sproles

Donald Veraska

Don Watt

Mary Zalar

Cotton & Wareham

Jet Propulsion Laboratory

University of Oklahoma, Science&

Public Policy Program

John C. Holmes, Publishing Officer

Kathie S. Boss Joanne Heming
Acknowledgment

This report would not be possible in its present form without the careful

review and information supplied by hundreds of individuals and companies in the

many fields and specialties covered by this report.

vi
Contents

Chapter Page

1.

I l .

Ill.

Iv.

v.

VI.

VIl.

Vlll.

lx.

x.

xl.

xl 1.

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Overview of Onsite Solar Technology and Summary of

Economic Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

FederaI Policy for Promoting and Regulating Onsite Solar Energy . . . . 59

Onsite Electric-Power Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

The Relationship Between Onsite Generation and Conventional

Public Utilities. ,..,. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

AppendixV-1.–Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . 161

Legal Aspects of Onsite Solar Facil

The lmpac of Solar Energy on U.S.

Environmental Quality . . . . . .

Collectors . . . . . . . . . . . .

ities. . . . . . . . . . . . . . . . . . . . . . . . . 175

Foreign Policy, Labor, and

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

. . . . . . . . . . . . . . . . . . . . . . . . . . 245

Appendix Vlll-A.–Techniques Used to ComputetheOutput

of Representative Collector Designs . . . . . . . . . . . . 303

EnergyConversion With Heat Engines . . . . . . . . . . . . . . . . . . . . . . . . . . 329

Energy Conversion With Photovoltaics .,...., . . . . . . . . . . . . . . . . . . 393

Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

Appendix XI-A.–A Technique for Estimating the Allowable

Cost of Storage Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487

Appendix Xl-B. —Analysis of Performance . . . . . . . . . . . . . . . . . . . . 488

Appendix Xl-C. —Costs of Designs Chosen for Analysis . . . . . . . . . . . 496

Heating and Cooling Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507

NOTE: This volume summarizes the analysis of system performance and costs,

discusses policy, major impacts and constraints on solar markets, and reviews direct solar

technology. Volume II discusses the analytical methods used and provides details on each

system analyzed.

vii
OVERVIEW
OVERVIEW

Page

Results of the Economic Analysis. . . . . . . . . . . . 3

Onsite Solar Technology . . . . . . . . . . . . . . . . . . . 5

Major Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

What Can the Federal Government Do?. . . . . . . 7
Overview

This assessment reviews the potential of a family of solar energy equipment called “onsite” energy systems because they are designed to be located on or near the buildings or groups of buildings which they provide with

heat or electricity. The technologies examined produce useful energy directly

from sunlight; equipment making indirect use of solar energy, such as wind

machines or devices using biological materials as a fuel, is not examined.

The technical feasibility of most direct, onsite solar energy systems has

been experimentally established. While onsite solar energy systems are competitive with conventional energy sources in a limited number of applications

today, widespread use will require demonstrating that projected cost reductions can be achieved. By the mid-1980’s, the range of costs which can be

reasonably forecast for energy from onsite energy devices will overlap the

range of costs forecast for energy from conventional sources for a variety of

residential, commercial, and industrial applications. An uncertainty inherent

in such comparisons is the price society will be willing to pay for the social

and environmental benefits of onsite solar energy.

If energy can be produced from onsite

solar energy systems at competitive prices,

the increasing centralization which has characterized the equipment and institutions

associated with energy industries for the

past 30 years could be dramatically altered;

basic patterns of energy consumption and

production could be changed; energy-producing equipment could be owned by many

types of organizations and even individual

homeowners. Given the increasing fraction

of U.S. industrial assets which are being invested in energy industries, tendencies

toward centralization of many aspects of

society couId also be affected.

The onsite solar energy industry is in most

cases a straightforward extension of existing

heating, cooling, and air-conditioning industries. It could clearly develop without

Federal participation. Unless a concerted effort is made to identify the special problems

of

1

onsite technology, remove reguIatory barriers, provide financial incentives, and support an aggressive research, development

and demonstration program, however, it is

unlikely that onsite equipment will be able

to contribute significantly to U.S. energy

supplies by the year 2000. With such support, it is possible that onsite solar devices

could be made competitive in markets representing over 40 percent of U.S. energy demand by the mid-1980s, although the output

of solar equipment installed by this date is

unlikely to be able to meet more than a

small fraction of this potential market. Existing Federal programs controlling fuel prices

and subsidizing nonsolar energy sources

have created a situation where, without

compensating subsidies, solar energy i s

uniquely disadvantaged. Federal support of

solar energy has concentrated disproportionate attention to central electric generating systems instead of exploiting the

special opportunities provided by onsite

equipment

RESULTS OF THE ECONOMIC ANALYSIS

Solar systems designed to provide domestic hot water (3,5 percent of U.S.

energy demand) are competitive with

electric hot water systems in most parts

of the United States today if comparisons are based on the average monthly

payments made for energy during the

life of the system. Solar space-heating

3
4 ● Solar Technology to Today’s Energy Needs

2.

3.

4.

5.

6.

for new residential and commercial

buildings (1 7.8 percent of U.S. energy demand) is somewhat less advanced but is,

or should soon be, marginally competitive with heat pump and electric resistance space heating in many areas of the

country.

On the same basis, solar space-heating

and hot water systems may be competitive with oil or gas delivered to typical

residential or commercial customers by

the mid-1980’s. The solar energy equipment should be competitive with heating

systems using synthetic oil and gas.

Solar energy from systems which provide

100 percent of the heating and hot water

required by large buildings or groups of

houses may not cost significantly more

than energy from systems designed to

meet 50 to 70 percent of these demands.

Cost reductions and improvements in the

performance of solar cells (photovoltaics), small engines powered from solar

sources, and solar collectors possible by

the mid-1 980’s may result in onsite solar

energy systems capable of producing

electricity for residential and commercial buildings for $0.04 to $0.10/kWh — a

price which would probably be competitive with electricity delivered to these

customers from conventional utilities.

Full exploration of the potential for

energy conservation and the use of simple “passive” solar space-conditioning

techniques should clearly precede any

attempt to use more complex solar energy equipment.

It will be possible to construct onsite

energy systems capable of supplying all

electrical and thermal energy needs of a

building from direct solar energy systems, but it wilI usualIy be less expensive

to rely on some other form of energy as a

backup if this alternative is available. In

some of the cases examined, the 100-

percent solar systems did not cost significantly more than smaller solar install a7

8

tions on a life-cycle cost basis; in other

cases, however, 100-percent solar systems were twice as expensive.

Providing backup electricity to onsite

solar energy systems may, in some cases,

cost electric utilities more per unit of

energy delivered than the average utility

cost. Solar energy systems are not

unique in this respect, however, since

many conventional buildings impose demands on electric utilities which adversely affect utility costs. When the real

incremental cost of producing electricity

for each type of building is computed,

the total cost of operating solar energy

systems backed up with conventional

electric utilities is, in many cases, comparable to the cost of operating conventional all-electric buildings. Most solar

heating systems are equipped with energy storage devices which, at a modest

additional expense, can be used to reduce or possibly eliminate most adverse

effects on electric utilities attribut

to solar demand patterns.

Existing rate structures and avail

metering equipment may not be

able

able

adequate to produce an acceptable pattern

of charging and discharging onsite storage equipment. As a result, onsite storage equipment may not be able to eliminate al I adverse affects of solar equipment on electric utilities. It is extremely

expensive to leave costly generating

equipment idle; large electric-generating

systems may therefore not be the most

attractive way to provide backup power

to onsite solar energy systems, particuIarly if the onsite devices generate electricity as well as thermal energy and lowcost electric storage is not available. The

best technique for providing backup

power requires a careful understanding

of the relative costs of onsite and centralized storage equipment, energy distribution costs, and the costs of maintaining standby generating capacity.

These costs vary greatly around the

country.
Overview ● 5

9. By the mid-1980’s, solar systems designed to provide agricuItural or industrial process heat at temperatures below

5500 F (2 to 7 percent of present U.S.

energy demand) will not be competitive

with direct combustion of coal in large

industries but may be an attractive alternative in situations where the direct use

of coal is expensive or restricted because

of environmental regulations, lack of access to coal supplies, or other factors.

10. The fact that onsite solar energy systems

are calculated to be competitive on the

basis of monthly costs does not mean

that these devices will rapidly penetrate

the market. The fraction of U.S. energy

supplies which onsite systems wit I supply

will depend on the extent to which customers make purchases on the basis of

operating costs (instead of comparing

ONSITE SOLAR

1. Onsite technology is not characterized by

a single dominant design concept but

rather by an enormous variety of competing approaches. Systems must be tailored to specific climates and applications. The equipment works best when the

building or industrial process which it

serves is designed to make the most efficient use of the solar resource.

2. There are no clear economies of scale in

solar collectors, solar cells, or in many

types of engines compatible with solar

energy, although there are economies of

scale in many kinds of energy storage

equipment. Small, distributed energy systems can readily “cogenerate” heat and

electricity and have several advantages

not easily expressed in conventional economic terms: relative ease of using lowtemperature heat, short construction

times which permit rapid adjustment to

changing energy demand; relatively small

investments in each installation; and efficient land use (since collectors can be

located on rooftops).

11.

only the initial purchase price), the rate

at which an infrastructure for manufacturing, installing, and supporting such

systems develops, the removal of regulatory barriers, and the incentives which

are avaiIable.

The small size of onsite solar equipment

does not preclude utility ownership,

although there may be regulatory problems associated with such an arrangement. Utilities can provide market aggregation and financing for systems

where building owners are unable to

raise capital. Utilities wilI uniquely compare the cost of energy from new solar

equipment with the cost of energy from

new conventional plants — energy which

typically is more expensive than the

average cost of energy delivered to utility customers.

TECHNOLOGY

3

4

Development of simple collectors– both

stationary systems and devices which

move, tracking the Sun — is of central importance. While a wide range of applications can probably be found for colIectors

which cost $7 to $12 per square foot, development of collectors costing $4 to $7

per square foot would greatly increase the

number of potential near-term uses for

solar energy equipment. The optical and

mechanical problems confronted in developing such devices will more probably

be overcome with patience and clever

designs than with fundamental research

breakthroughs.

The potential of low-cost thermal storage

has not been adequately explored. This

shouId make possible solar heating systems requiring no backup energy. Development of a chemical reaction capable of

storing solar energy efficiently and economicalIy in chemical form would greatly

expand the potential uses of solar energy.

Neither approach has been given adequate priority.
6 . Solar Technology to Today’s Energy Needs

5. The cost of solar cells can be reduced by

mass producing current silicon cell

designs, developing thin films of amorphous silicon material, cadmium sulfide,

or other materials with acceptable efficiencies, or by designing low-cost optical

systems to focus Iight on high-efficiency

cells. Solar engines can be designed to

operate at 1300 to 2000 F using machines

that are essentially refrigerators running

backward, at intermediate temperatures

(using standard steam engines and advanced designs), and at high temperatures

(1,400 0 F) using Stirling engines and other

machines with potentially high efficiencies. A funding strategy must be devel6.

7.

oped which amounts to a system for placing bets on a broad spectrum of schemes.

There is a large overlap between technology developed for onsite solar energy

systems and technology developed to improve the efficiency of using conventional energy sources — particularly in

energy storage and engine design.

No major technical problems should be

encountered in connecting solar thermal

or solar electric systems to electric utility

grids. Utilities should be able to purchase

excess electricity generated in onsite units

for 25 to 100 percent of the price they

charge for electricity.

MAJOR IMPACTS

1. Onsite solar energy services can be easily

integrated into the existing construction

and heating, ventilating, and air-conditioning industries. The equipment can be

manufactured, installed, maintained, financed, and insured by the organizations

and individuals now performing the same

services for conventional heating and

cooling and industrial equipment.

2. If small solar energy systems prove economically attractive, the concept of the

“natural monopoly” of existing utilities

wouId need to be reviewed.

3. The widespread use of onsite equipment

would increase the number of jobs required to generate energy. Jobs would be

created because imported oil would be

replaced with energy from domestically

produced solar equipment and because

solar energy is more labor intensive than

energy from conventional sources. The

new jobs would be primarily in construction trades, metals, and chemicals. They

would tend to be located where such jobs

now exist and should provide a relatively

stable source of employment, The longterm implications of a shift to laborintensive energy sources, however, are not

welI understood.

4. Solar energy systems produce far less aggregate air and water pollution during

their manufacture and operating Iifetimes

than energy systems based on fossil fuels.

Solar equipment may be a particularly attractive energy source in areas where increases in emissions are prohibited. The

major environmental problem of solar

equipment is the use of land. However,

this impact on land use can be minimized

by carefully integrating solar collectors

into building designs, but densely populated urban and suburban communities

may have regions where shade from trees

or buildings make the use of onsite solar

energy unattractive.

5. Widespread use of solar energy worldwide could greatly reduce tensions associated with world competition over diminishing sources of fossil fuels without encouraging the use of technologies which

increase the risk of nuclear weapons proliferation. Growth of a solar industry

wouId reduce imports and encourage investments in the U.S. economy,
WHAT CAN THE FEDERAL GOVERNMENT DO?

1

2

3

4

The most straightforward, but politically

the most dIfficuIt, approach to stimulating markets for onsite solar energy

wouId be to remove prlce controls and implicit subsidies granted to conventional

energy sources, and aIlow energy prices to

rise to the cost of energy from new prod u c t Ion f a c i I i t i es

The marketing of solar equipment could

be seriously disrupted if incompetent or

unethical dealers give the technology a

reputation for poor performance Performance standards and uniform testing

procedures must be developed rapidly to

prevent abuses It is necessary, however,

that these standards be continually updated to keep pace with a rapidly moving

technology and to insure that the regulations do not inadvertently discriminate

against new concepts

Investment tax credits, low-interest loans,

exempt ions from property tax, and accelerated depreciation aIlowances on solar

equipment can significantly reduce the

cost of solar energy perceived by prospective buyers No one program will work

equally well to provide incentives for all

systems to a I I types of owners, SimiIar

kinds of incentives applied to manufacturers could be used to reduce the price

of solar equipment.

Regulations governing the rates at which

energy is sold to and purchased from onsite energy systems need to be developed

5

6

7,

8.

rapidIy, ReguIations preventing nonutility

ownership of onsite generating equip -

ment, and interfering with utiIity ownership of onsite energy equipment need to

be reviewed and updated.

A variety of Federal subsidy programs

already exist which can be modified to encourage the use of solar energy systems

The use of solar equipment on Federal instalIations can stimulate sales and reduce

costs,

A significant amount of basic research

and advanced development work remains

to be done. Promising areas of research

were noted in the previous discussion of

onsite technology

The U.S. program in onsite solar energy

couId be improved through closer cooperation with foreign programs. Many

types of onsite solar energy are likely to

be economically attractive abroad before

they enter commercial markets in the

United States. It is unlikely that other nations will move rapidly to integrate solar

energy options into their energy planning

unless the United States makes a major

commitment to use of solar energy.

Perhaps the most important step which

can be taken with respect to onsite solar

energy is to insure that the advantages of

the onsite approaches are seriousl y considered in constructing overalI U.S, energy

planning,
Chapter I

INTRODUCTION
Chapter l.— INTRODUCTION

Page

Onsite Solar Technology ...................15

Techniques for Assessing Onsite

Technology . . . . . . . . . . . . . . . . . . . .......15

integration of Onsite Facilities With

Other Energy Sources. . . . . . . . . . . .......15

Research and Development . . . . . . . . .......17

Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

PossibIe lmpacts of Onsite Solar Energy. .....22

U.S. Security and World Trade . . . . . . .......22

Labor . . . . . . . . . . . . . . . . . . . . . . . . . . . .......22

Utility Participation. . . . . . . . . . . . . . . .......23

Environment and Land Use . . . . . . . . .......23

Page

Federal Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Standards . . . . . . . . . . . . . . . . . . . . . . . .......25

Other Specialized Legal and Regulatory

Problems . . . . . . . . . . . . . . . . . . . . . .......25

Comparison With Current Policy. . . . .......26

LIST OF TABLES

Table No. Page

l. The Potential of Onsite Solar Energy

Equipment . . . . . . . . . . . . . . . . . . . . . . .......19
Chapter I

Introduction

Small solar energy units attached to or located near individual buildings,

industries, or groups of buildings (called “onsite” energy systems throughout this work) must be considered potentially important additions to the

limited number of opportunities for meeting the world’s demand for energy

both in the next few decades and into the indefinite future. This study examines a set of these technologies characterized by the fact that they convert

the Sun’s energy directly into useful thermal and electric energy; the study

does not examine wind power, systems using biological materials as fuels, or

other concepts for using the Sun’s energy indirectly.

The major barrier to the widespread use of onsite solar energy is its cost.

Developments in research can lead to reduced costs and improved performance, but the fundamental feasibility of the technology is well established.

Onsite solar devices are technicality capable of meeting virtually all residential, commercial, and industrial energy requirements; they can provide

heating and air-conditioning, hot water for residences, heating for industrial

and agricuItural processes, and mechanical and electrical power.

The energy supplied by these systems is expensive by today’s standards.

The extent to which this continues to be a barrier depends in part on the success of numerous programs designed to reduce the cost of solar equipment.

It will also depend heavily on changes in the price of conventional energy.

The market for new types of energy producing and consuming devices is likely to change rapidly in the next two decades as energy costs increase and

become a major concern. In many ways it is easier to make confident predictions about the future costs of solar energy—which depend for the most part

on predictable manufacturing techniques —than it is to estimate the cost of

fuels whose price may depend on monopoly price manipulation, international

competition over diminishing energy supplies, the stringency of federally

imposed environmental controls, and other problems which are difficult to

anticipate.

The issue of costs is treated in much more

detail in later sections of this report, but the

only fair way to summarize the results of the

analysis is to note that the range of possible

costs of solar energy overlaps the range of

possible costs of energy from conventional

sources in a large number of cases. It is

simply not possible to make dogmatic statements about the conclusions. The significance of the fact that solar and nonsolar

costs overlap, however, should not be underestimated since this overlap means that it

may be necessary to choose future energy

options on the basis of criteria other than

the estimates of future costs (the cost analysis being indecisive). At a minimum it implies that the solar energy alternative should

be supported with at least as much attention

and care as other options for meeting energy

needs in the future.

The analysis indicated, for example, that

solar systems for providing domestic hot

water and building heat are marginally competitive with electric heating in many parts

of the Nation today, These systems may be

competitive with oiI and gas (where it is

available) in many parts of the country

with; n a decade if solar prices fall and the

price of oil and gas rises at rates which appear in reasonable forecasts. Solar equipment should be able to compete with synthetic fuels. Electricity from solar sources is

now only attractive in remote areas where

alternate energy sources are very expensive.

There are sound reasons to speculate, how11
12 ● Solar Technology to Today’s Energy Needs

ever, that the price of solar electricity may

fall by a factor of 15 or more by the mid1980’s and reach a price where solar electric

devices could be installed to provide supplemental electricity to houses and commercial buildings.

Inflation resulting from increases in energy prices may have the effect of offsetting

some of the cost reductions expected from

new designs. It is entirely possible, however,

that even the price of solar equipment now

in mass production will rise more slowly

than the price of conventional energy. Processes used to manufacture the components

of solar devices are Iikely to make more efficient use of energy if energy prices rise since

there is clearly considerable room for improving the energy efficiency of American

industry. The design of solar devices can

also be changed to minimize the use of components whose costs are linked most closely

to energy costs. Frames for solar collectors,

for example, can be made from steel, aluminum, concrete, plastic, wood, and many

other materials. Ultimately, of course, it

would be possible to manufacture solar

equipment using solar energy.

A number of the advantages of solar

energy equipment are not comfortably expressed in the strict economic terms discussed above. For example, widespread use

of onsite solar equipment could have a favorable impact on American labor — by creating attractive new jobs, on international

stability — by easing the competition for

conventional energy sources without increasing opportunities for proliferation of

nuclear weapons, and on the environment —

by replacing polluting energy sources.

(These advantages are discussed at some

length in chapter `Vii.) The use of solar

energy during the next two decades wilI depend largely on the value which society attaches to these advantages.

Widespread use of onsite solar equipment

[or indeed of onsite energy equipment of

any kind) would reverse a 40-year trend

toward centralization of energy sources.

The larger plants tended to be less expensive

to build per unit of output, more efficient,

and able to use a greater variety of fuels.

Siting problems (for large plants) tended to

be minimized by the ability to choose a few

remote locations. Conventionally fueled onsite facilities were often abandoned because

their owners were concerned about the cost

of maintaining equipment and the chance

that a system failure would be expensive. lnvestments in onsite equipment were usually

not as attractive as investments in areas

more directly related to the business and a

feeling emerged that energy generation was

best left to the expertise of utilities. As a

result, most design improvements in the past

few decades have occurred in the technology of larger generating equipment, and the

bulk of Federal research activity in energy

has been conducted in large systems.

There are, however, reasons to suppose

that the unique nature of onsite solar energy

equipment may offset some of the advantages which impelled centralization:

●

●

●

The basic solar resource is distributed.

Solar units on individual buildings

could in some cases reduce transmission and distribution costs and losses.

Integrating the equipment with a building roof or with a parking facility can

minimize the land required for solar

equipment.

Location of equipment onsite greatly

increases design opportunities and

makes it easier to match the energy

equipment designs to specific onsite

energy demands; in particular, it is

easier to use the thermal output of the

collectors. A great deal of overlap exists between techniques and devices being developed for onsite solar systems

and equipment used for energy conservation. The solar designs are usually

most successful when integrated into a

coherent plan for matching energy resources to the end use.

Smaller equipment can be built more

quickly than larger facilities, thereby

reducing interest and inflation during

construction. This equipment can be

added in relatively modest increments.
Ch I Introduction 13

●

In

Iems

tant

fers

Onsite systems can also match reliability to local needs. A highly sophisticated industry, for example, may not

be able to tolerate power failures lasting a few hours per year while some

areas in developing countries may be

very pleased with systems which may

not provide power for a few days each

year—particularly if there are significant savings associated with accepting

this level of reliability. Centralized

systems force all customers to accept

the highest level of reliability demanded by any customer.

evaluating the advantages and probof onsite solar equipment, it is importo recognize that solar equipment diffrom conventional systems in several

significant ways:

In the first place, the systems which are

examined in this study do not really represent a single technology, but rather an enormous range of technologies, A great variety

of equipment components have been developed (many of which are reviewed in later

sections of this study) and these components can be combined in many different

ways to meet specific energy requirements

in specific climates.

A second unique characteristic of onsite

systems is the number of arrangements

which can be made for owning and operating onsite equipment, The small scale of the

devices makes it possible for individuals or

institutions other than utilities and major oil

companies to invest in equipment capable

of generating useful energy. This does not

necessarily mean that investor-owned utilities will not play a useful role in the development of the technology; there are cases

where there may be advantages associated

with utility ownership and maintenance of

onsite equipment. It is also possible that

municipal utilities, nonregulated companies

selling or renting onsite equipment, or even

neighborhood cooperatives will play a role

in owning and managing the equipment,

Each of these possibilities raises different

legal and regulatory issues.

Another singular feature of the small solar

devices is that, in comparison to larger energy equipment, they are relatively unsophisticated and would probably be manufactured, financed, insured, and maintained by

the people and institutions now performing

the same kinds of services for conventional

heating and cooling systems or industrial

equipment.

A fourth distinction between using solar

energy and energy derived from conventional fossil fuels is that the cost of solar

energy typically depends on temperature

and on when the energy is needed. Solar

energy is best suited for meeting energy

demands during daylight hours. Fossil fuels

typically burn at temperatures near 2,000 ‘C,

whether this high temperature is needed or

not. There is no great penalty associated

with operating an industrial process at high

temperatures up to this threshold. While

solar energy can provide high temperatures

(indeed, one of the first sophisticated uses

of direct solar energy was a facility for hightemperature metallurgy), fluids at such temperatures are expensive to collect, transport,

and store. The implications of having energy

costs depend on temperature and time have

never been seriously evaluated. It is an issue

which may be of increasing concern regardless of whether solar energy is used, since

there are many ways of recovering relatively

low-temperature energy from commercial

and industrial processes. If an economy

began to reflect this new set of costs, the

relative values of energy-intensive materials

and sources could change significantly. It

may be necessary to reevaluate the techniques used for each industrial process to

make maximum use of the solar resource.

(Development of a successful thermochemical or photochemical reaction which

can use solar collectors to produce chemicals capable of being transported, stored,

and later reacted to produce high temperatures would do much to eliminate the penalty paid for high-temperature solar energy.)

While the cost of solar energy may depend on temperature, it may not depend on
14 ● Solar Technology to Today’s Energy Needs

the size of the system employed. Economies

of scale in solar equipment are very difficult

to establish, particularly if it is possible to

connect several small generating and consuming facilities with a common electrical

or thermal distribution system.

Solar collectors are generally modular

and typically the only economies of scale in

coIIector arrays resuIt from price reductions

obtained through large single purchases.

This also applies to solar cells used to generate electricity since even the largest solar

cell systems consist of arrays of small, individual generating units. Large heat engines

are typically less expensive per unit of output than small systems of identical design,

but the cost of these engines is typically a

small part of the overall cost of the solar

energy system; the cost of these systems is

usually dominated by the price paid for collectors. It may also be possible to produce

small heat engines which are as efficient as

larger engines. The cost per unit of output

could be comparable to that of large engines if mass-production techniques are

used. Many types of storage systems, however, do show significant economies of scale

at least up to a size where they are capable

of storing enough energy for several hundred typical residences. Much more work

needs to be done to determine the best size

and placement of storage devices of all

kinds.

All onsite solar facilities will face the difficulties which have led to the steady decline in conventional onsite generating faciiities: poorly engineered designs, inability of

organizations other than utilities to raise

capital for investments with relatively long

payback times, uncertainties about maintenance costs, and numerous other concerns.

Given the uncertainties inherent in an analysis of this type, it was simply not possible

to establish that there either clearly were or

were not economic advantages for small

solar systems.

Even if onsite solar energy systems could

be unambiguously shown to be a preferred

energy source, it is clear that they would

have a long way to go before they could provide a major fraction of the energy used in

the United States, For example, the combined output of all solar heating and hot

water systems used in the United States during 1977 displaced about 1 billion kilowatt

hours of thermal energy and this is less than

1/200 of 1 percent of total U.S. energy requirements in 1977. The peak electrical output of all solar electric systems was about

1,500 kilowatts. Starting from this small

base, solar sales would need to increase by

about 50 percent per year for 20 years to

achieve an output equivalent to 10 percent

of U.S. energy requirements. Achieving this

level of output would require an investment

of more than $500 biIIion.

While the growth rates and the investments required to increase use of onsite

equipment seem ambitious, and would

clearly require an enormous growth in the

infrastructure of manufacturers, installers,

and salesmen needed to make, market, finance, and service the solar equipment, it

must be recognized that any technology

which will supply a large fraction of U.S.

energy needs by the turn of the century will

require an enormous growth rate and investment; yet some new technology must be

available during this period as the world

reaches the physical Iimits of low-cost supplies of oil and gas. The transition cannot be

a painless one since all of the new energy

sources are Iikely to be more expensive than

current energy. The major remaining question is whether we will be able to take advantage of the warning which the geologists

have given us, reflect on the options available, explore their potential, and prepare a

strategy for a graceful transition to energy

sources we can live with, or, whether energy

policy will be guided by inadvertence,

chance, and reactions to sudden crises and

shortages.

The remainder of this study is devoted to

defining the circumstances in which onsite

solar technologies, with their rather curious

set of characteristics, could play a significant role in supplying energy. It examines

the technical opportunities now available

and under development; reviews the current
Ch. I Introduction ● 1 5

and potential future cost of integrated systems based on these technologies operating

in several representative cities in the United

States; explores the legal and regulatory

problems encountered by operators of small

generating equipment units; tries to explain

the impact which widespread use of onsite

solar technology might have on the quality

of the environment, on the American labor

force, and on the achievement of major U.S.

foreign policy objectives; and finally, it attempts to define the role and responsibility

of the Federal Government in reguIating and

promoting the technology. Some of the major results of this analysis are outlined in the

present chapter.

ONSITE SOLAR TECHNOLOGY

Adequately assessing the opportunities

presented by onsite technology is enormously difficult because there is such a diversity of approaches, many of which have

never been adequately investigated. The

number of options is increased by the fact

that, by its nature, onsite equipment is

tailored to specific applications in specific

climates, since the equipment is much more

efficient if care is taken to integrate the onsite equipment into the building or industrial apparatus to which it provides energy.

The number of technical alternatives in

onsite solar equipment is astonishingly

great, in part because research in these

areas is on a scale where a smalI firm or individual inventors can develop useful concepts. Concepts have been developed by

groups ranging from backyard inventors to

well-funded Government and industrial laboratories. More than 200 firms are now

manufacturing solar coIIectors, and competition will probably eliminate many of the

products on the market, This fact presents a

particularly difficult problem for Federal

planners attempting to develop a coherent

research program.

TECHNIQUES FOR ASSESSING

ONSITE TECHNOLOGY

It is important to compare competing

technologies on the basis of their ability to

perform a specific set of tasks in a specific

location – generalizations and simple “measures of merit” can be very misleading. This

is particularly true when the costs of onsite

systems are compared with the cost of centralized generating facilities; an accurate

estimate of the cost of energy from a central

unit should include an analysis of all losses

in transmission and inefficiencies encountered when the energy from the central facility is converted to useful energy at the site.

In the analysis presented in this report, systems have been compared on the basis of

their ability to meet all of the energy requirements of a single family house, an

apartment building, and other defined patterns of energy consumption. Computer

analysis has been used to evaluate the performance of equipment operating in Albuquerque, N. Mex., Boston, Mass., Fort Worth,

Tex., and Omaha, Nebr. The performance of

a system component cannot be fairly evaluated without examining its performance as

a part of an integrated system. The utility of

a collector design, for example, cannot be

assessed without understanding how it will

perform when connected to thermal storage

devices and subjected to the winds, temperature changes, cloud patterns, and fluctuating energy demands that characterize

actual installations.

INTEGRATION OF ONSITE FACILITIES

WITH OTHER ENERGY SOURCES

Carrying the logic of this thesis one step

further, it can be seen that it is also necessary to review the performance of onsite

energy equipment as an element of a system
16 ● Solar Technology to Today’s Energy Needs

capable of providing all of the energy requirements of a region. Because most onsite

devices will be connected with conventional

energy sources which provide backup power, the performance characteristics of the

onsite devices can affect costs of energy delivered to all parts of the community. This is

particularly true if electricity is used to provide backup power since the cost of electric

power increases significantly if it is required

to meet irregular demands; it is very costly

to maintain generating equipment which

will only be used during cloudy periods.

The question of providing backup power

to solar energy systems is intimately connected with the problem of determining

whether energy generated from onsite solar

equipment should be stored, or whether it

should be transmitted to other consumers

who may have a need for the excess onsite

energy. Analysis conducted for this study indicates that it is usually preferable to allow

the onsite unit to sell energy to a community-wide electric distribution grid than to

store the excess electricity in onsite battery

equipment (although this result could be

reversed if very low-cost batteries are developed). In general, if energy transmission is

relatively inexpensive, it is preferable to

connect as many customers and producers

together as possible. The value of the excess

energy sold from onsite generating equipment depends on the nature of the conventional generating equipment in the region,

the local climate, and a number of other factors. The analysis indicates that electric

companies shouId be able to purchase excess electricity generated by residential and

commercial onsite solar facilities for 25 to

100 percent of the price at which they sell

energy. Determining a just rate for purchases and sales can be extremely complex

and in some States, legal and regulatory

problems may have to be overcome to

achieve a just relationship. Presently few

utilities are willing to purchase energy from

onsite generating systems. (These issues are

discussed in detail in chapters V and VI.)

None of the technical problems associated with connections to existing electrical grids should present major problems.

Relatively inexpensive devices are on the

market which will disconnect onsite equipment from utility Iines so that Iinemen can

perform repairs safely, and meters are available which can monitor the production of

thermal energy and the purchase and sale of

energy from onsite systems. Moreover, onsite equipment should not create insurmountable load management problems for

utilities, even if a relatively large number of

their customers use onsite devices.

The relatively low cost of onsite thermal

energy storage creates a situation where it

may be preferable to store electrical energy

generated in central electric-generating facilities during the night (when electric

demands are low) in onsite thermal storage

when this energy is to be used for heating.

The storage tanks typically associated with

solar heating systems provide an ideal opportunity for this kind of storage but conventional buildings can be equipped with

storage facilities which are charged only

with electricity from conventional sources.

When a careful analysis is made of all of the

costs incurred in meeting the energy needs

of typical buildings (including both onsite

costs and the real costs undertaken to provide backup power) it appears that costs of

both solar and conventional buildings are

reduced when energy used for heating (or

backup heating for the solar system) is

stored onsite during periods when demands

on the electric utilities are low. The costs of

conventional systems were reduced more

than the costs of the solar systems, however,

and solar heating systems compared less favorably with conventional systems when

these methods were used. There were, however, a number of cases where the solar

equipment still was economicalIy preferable.

It is important to recognize that while the

relatively uneven loads imposed by providing backup power to solar energy equipment can have an adverse effect on overall

utility costs, many other kinds of energyconsuming devices also impose very uneven

loads on a utility. Insulating a building, for
Ch. I Introduction ● 1 7

example, tends not to decrease the peak

electrical demand significantly during the

summer (the period when most utility peaks

are highest), but does decrease demands

during the winter, resulting in increased

utility costs. Similarly, electric heat pumps

impose much more uneven loads than baseboard resistance heating. (In fact, when all

costs are evaluated, heat pumps may be

more expensive to operate than electric

resistance heating systems which purchase

electricity only at night. )

In evaluating costs, it was assumed that

the electric utility used a set of central

generating systems which were optimally

chosen to meet each type of demand, This is

the only valid way to compare costs over the

long term, It is tautological that equipment

designed to minimize costs for a conventional load pattern will be less efficient if it

is used to meet a different load pattern (e. g.,

loads which include a large amount of solar

backup demands). Admittedly, regulatory

delays and the mortmain of existing plants

and equipment will always prevent utilities

from optimizing their facilities to new load

patterns over the short term.

There are circumstances where it may be

preferable to transmit thermal energy rather

than to store it onsite since there are very

significant economies of scale in thermal

storage. The analysis in this study discovered several areas where 100 percent of the

heating and hot water requirements of individual houses could be met by solar energy if a number of homes were connected to

a large central storage tank. Distributing

energy in thermal form instead of electrical

form was also found to be attractive in a

number of conventional solar energy systems designed to meet all of the energy

needs of a large community. I n these cases,

the thermal energy was very inexpensive

because it was a byproduct of generating

electricity and the bulk of the cost of the

energy was the cost of delivery.

The difficulties encountered in providing

backup power from electric utilities to onsite solar facilities, characterized by large,

expensive generating equipment, may create a situation where it is preferable to provide backup entirely from natural or even

synthetic oil or gas. In several cases examined, it was less expensive to provide backup from these chemical sources than from

electricity even if it was assumed that the

chemical systems’ fuels increased rapidly in

price.

RESEARCH AND DEVELOPMENT

in a surprising number of cases, onsite

solar technologies are not economically attractive because of the high costs of such

mundane processes as instalIing and aligning collectors and bending metal in fabricating facilities. If these costs cannot be reduced with some ingenious procedures, it is

difficult to imagine a research breakthrough

which would radically reduce the cost of

solar energy derived from such systems. If

these costs can be reduced, a number of attractive devices are possible with existing

technology. What is needed is perhaps more

the genius of the man who invented the zipper than the genius of an Einstein.

There are a number of areas where research and development seem particularly

important.

●

●

●

●

●

Determining the best way to design a

building structure to maximize natural

heating and cooling,

Developing simple collectors from extremely low-cost materials (e. g., cheap,

durable plastic films),

Developing techniques for reducing the

cost of manufacturing simple tracking

and concentrating collectors,

Developing economical techniques for

storing large amounts of energy in hot

water or rocks in order to meet all of

the annua l thermal demands o f

buildings,

Improving techniques and materials for

laying insulated pipes for thermal

distribution systems,
18 ● Solar Technology to Today’s Energy Needs

● Developing chemical reactions which I ing at very high temperatures (e. g.,

can be used to store or transfer ther

energy,

• Developing advanced electrochem

storage devices,

m a l

ical

● Designing an inexpensive and reliable

heat engine capable of working at

relatively low temperatures (e. g., below

2500 F),

● Designing an inexpensive, reliable,

high-efficiency engine capable of work1,4000 to 2,0000 F),

● Developing low-cost materials for solar

cells, and

● Developing dyes for a simple concentrating collector.

It is also vitally important that a strong

program in basic research accompany these

applied development projects. Research in

sol id state physics, surface chemistry, metalIurgy, thermochemical and photochemical

reactions and heat transfer is of particular

interest.

ECONOMICS

Table l-l indicates the size of different

energy markets in the United States, summarizes the potential of direct solar energy

in each market, and estimates when solar

equipment could begin to enter this market.

Direct onsite solar energy equipment is

likely to make its first major impact by providing supplemental heat and hot water for

residential and commercial buildings. This is

not an insignificant market since demand

for energy in this category represented

about 20 percent of all energy consumed in

the United States in 1975. There is already a

growing market for solar hot water systems

in regions with plentiful sunlight and high

electric rates where natural gas is not available for new buildings. A market for solar

heating systems is also developing in these

areas. If it was assumed that electric rates

increased 45 percent by the year 2000, solar

heating and hot water systems with plausible near-term costs showed lower life-cycle

costs than heat-pump systems in houses in

three of the four cities examined in this

study. The solar system was competitive in

all four cities when a 20-percent investment

tax credit was given to the solar system.

Solar energy was found to become an attractive alternative to oil and gas heating of

hot water in the mid-1980’s, if consumers are

convinced that oil prices will increase to $23

to $35 per barrel by the year 2000, or that

gas prices will reach an equivalent level.

Fuel prices would probably rise at least as

rapidly as this if a major fraction of U.S. liquid fuels were derived from synthetic

sources by the year 2000.

Most of the solar heating and hot water

systems installed today are not capable of

meeting all of the heating requirements of

the buildings they serve; a conventional furnace or baseboard heaters must be used during periods of prolonged cloudiness. This

limits the fraction of the energy consumed

for building heat which solar devices can

replace. It is possible, however, to construct

solar systems providing 100 percent of a

building’s heating demands by using a sufficiently large storage facility. The analysis

conducted for this study indicated that

within 3 to 5 years it should be possible to

construct systems capable of supplying all

of the heating and hot water requirements

of large buildings at prices which would be

competitive with conventional electric heating in three of the four cities examined. The

systems would be competitive in all four

cities if a 20-percent investment tax credit

was granted to the solar equipment.
Ch. I Introduction ● 19

Table I-1.—The Potential of Onsite Solar Energy Equipment

Demand type

1. RESIDENTIAL AND COMMERCIAL

a. Hot water

b. Space-heating

c. Electricity for lighting and other

miscellaneous demands

d. Air-conditioning

e. Gas cooking and other

miscellaneous uses

Il. TRANSPORTATION

Ill. INDUSTRY

a. Electric motor drives,

electrolytics, & misc.

electrical demands

b. Process heat at temperatures

below 2120 F

c. Process heat at temperatures

of 2120 to 5500 F

d. Process heat at temperatures

greater than 550° F

e. Chemical feedstocks

Percentage of

total U.S.

energy demand Potential of onslte solar

in 1975 energy equipment

(36)

3.5

17.8

9.0

4.3

1.2

(26)

(38)

8.7

2.0 (7.0)’

5.3 (6.5)*

18.6 (12.4)* ●

3.3

Competitive now with electric hot water heating on

life-cycle cost basis and with oil and gas if year 2000

prices expected to reach$15-20/bbl equivalent.

Combined hot water and heating systems marginally

competitive with resistance heating and heat pumps

now or in the near future, competitive with oil and gas if

solar prices drop, or, if year 2000 prices expected to

reach $23-35/bbl equivalent. Many ‘‘passive” approaches

clearly attractive.

Possibly competitive by mid- to late-1980’s if electric

rates increase by 50 percent by the year 2000.

Competitive in remote areas today.

Some systems available, but economically attractive

systems unlikely until early or mid-1980’s.

Cooking conveniently available from direct solar

sources only through electricity.

No major role probable for direct, solar energy. Some

market possible for electric vehicles charged from onsite electric systems or vehicles using chemical energy

generated on site.

Penetration of this market unlikely until 1990’s unless

research progresses faster than expected. Solar

cogeneration systems may be attractive in some areas

by the mid-1980’s.

Possibly competitive with oil and gas by 1980’s if prices

are expected to increase to $14-16/bbl equivalent by the

year 2000. Competition with direct combustion of coal

unlikely in large plants unless conversion to coal is very

expensive.

Possibly competitive in 1980’s with oil and gas if

prices reach $19-25/bbl equivalent by 1985 and

$30-40/bbl by 2000.

Probably competitive only when onsite solar energy for

electric motor drives is competitive.

No market for direct solar energy.

“If heat used to raise the temperature of materials from 600 F IS Included

. . Nearly 90 percent of the process heat used at these temperatures IS consumed In blast fUrnaCe% steel mills! stone, 91a5S, and clay processing, and

petroleum reflnlng

SOURCES. Total energy requirements for Industry, transportation, restdentlal, and commercial consumers obtained from U S Department of the Interior

(Bureau of Mines) News Release March 14, 1977

Details for residential and commercial consumption patterns obtained from

J R Jackson and W S Johnson, Cornnrercla/ Errergy Use A Dlsaggregat{on by Fue/, Bui/dlrrg Type, and End Use, Oak R[dge National

Laboratory (ORNLICON-14) February 1978, page 9

E Hlrst and J Carney, Resldent~a/ Energy Use to the Year 2000 Conservation and Econorrr(cs, Oak Ridge Nat!onal Laboratory

(ORNUCON 13) September 1977, page 9

Details of Industrial energy consumption based on

D S Freeman, (ed ) A Tlrne fo Choose, Balllnger, Cambridge, Mass , 1974, p 456

InterTechnology Corporation, Ana/ysls of /he Econornlc Potentfa/ of .So/ar T/rerrna/ Energy fo Pfovlde /ndusfrla/ Process F/eaf (ERDA

COO/2829.1}, p 53 (This survey Included Institutions using 59 percent of U S Industrial process heat )
20 ● solar Technology to Today’s Energy Needs

Electricity used in residences and commercial facilities for lighting, television sets,

dishwashers, and other appliances is expected to represent about 9 percent of the

primary energy consumed in the United

States in 1985. Residences and commercial

buildings pay the highest rates for electricity

since these rates must include charges for

the costly equipment needed to distribute

the electricity to a large number of small

consumers. It is likely, therefore, that devices for generating electricity from sunlight

will find their first large markets in this sector. (Solar electric devices will find substantial markets in remote military outposts, signalling devices, and other installations

before the large residential market can be

approached. The market for systems in

remote areas could, however, amount to

several hundred millions of dollars of annual sales, particularly if markets in nonindustrial countries can be captured.) Within

10 to 15 years it may be possible to develop

onsite solar devices capable of producing

electricity for $0.04 to $0.10/khVh, rates

which may be competitive with the cost of

electricity delivered to residential and commercial customers from new utility generating plants.

There is also a potentially large market

for direct solar energy equipment in industry

and agriculture. Table l-l indicates that 2 to

7 percent of U.S. energy is consumed in

these sectors at temperatures below the

boiling point of water, and 7 to 13 percent is

consumed at temperatures below 3500 F.

Solar equipment is now available which can

easily provide fluids or direct heating at

these temperatures. In many ways, industrial and agricultural markets are more

attractive than the residential and commercial markets since the residential and commercial customers are much more diverse

and will probably require a more complex

and expensive infrastructure for sales and

installation. The larger customers are also

likely to be confronted with gas curtailments during the next decade and will be in

the process of selecting a replacement for

natural gas.

There are, however, several major obstacles to solar use in industry and agriculture.

Consumers in these categories can use a variety of different conventional fuels (many

can burn coal directly) and pay much less

for electricity than residential and commercial customers. Moreover, they typically expect payback times on the order of 1 to 3

years for investments in new plant equipment. The cost of industrial solar heat can

also be somewhat higher than solar heat

provided for homes and residences if it is necessary to install collectors in fields where

land, footings, and other aspects of site

preparation must be charged to the solar

equipment and where piping heat to the factory can be expensive. Smaller installations

can be supported by building roofs and heat

is generated close to the site where the

energy is used.

Analysis of the cost of providing electricity and process heat to a large three-shift industry from different kinds of energy equipment which began operating in 1985 indicated that direct solar heat for low-temperature applications would be competitive with

oil if it was assumed that oil prices increase

to $15 to $20 per barrel by the year 2000 a nd

if the solar equipment is financed by a private utility. Solar heat at temperatures in

the range of 3500 F was competitive only if

it was assumed that oil prices reach $19 to

$25 per barrel by 1985, and are $30 to $40

per barrel by 2000. Competition with natural

gas and coal was possible for systems starting in 1985 only if it was assumed that the

prices of these fuels increase by a factor of

nearly three (from 1976 levels) by the year

2000 (e.g., coal costing $60 per ton). While

such price increases are possible for natural

gas, it seems unlikely that coal prices will increase at this rate. It is also possible that

solar heat at temperatures below 5000 to

6000 F will be competitive with heat derived

from synthetic hydrocarbons made from

coal.

While most solar heating systems for large

industrial or agricultural facilities may not

be fully competitive with conventional fuels
Ch. I Introduction ● 2 1

before the mid-1980’s, it will almost certainly be possible to find industries whose specific problems are well suited to the use of

solar energy in the near future. There may

welI be a large near-term market for grain

drying systems in less-developed countries,

for example. Near-term markets for solar

equipment in the industrial sector could

also result from existing environmental

legislation; solar energy may prove to be an

attractive way to expand industrial capacity

while minimizing increases in emissions.

Solar cogeneration devices using solar

cells or Stirling engines may be attractive in

roughly the same circumstances that found

solar hot water competitive, although the

solar systems were less attractive when compared with cogeneration systems using conventional fuels. It seemed unlikely that solar

electric systems which did not cogenerate

would be able to compete with the low cost

of electricity delivered to industrial facilities from conventional sources until at least

the mid-1 990’s, although unexpected progress in research could well accelerate the

rate at which the solar electric systems

become competitive.

Solar energy used for direct heat in blast

furnaces, glass plants, and other facilities requiring heat at very high temperatures (uses

representing 12 to 19 percent of U.S. energy

consumption) are unlikely to be competitive

before solar electric systems. Development

of an efficient thermochemical process,

which could be conducted in a solar collector and reversed in a special burner at high

temperature when heat is needed, would

greatly improve the prospects for using

direct solar energy in high-temperature applications.

Direct solar energy is unlikely to be used

as a substitute for any of the chemical

feedstocks which now consume about 3 percent of U.S. energy. Biomass would clearly

seem to be the preferred solar source for

feed stocks.

Similarly, transportation, which consumes

about 25 percent of U.S. energy, is unlikely

to provide a major near-term market for onsite direct solar energy. There may be some

circumstances where electric vehicles could

be charged from solar-generated electricity.

Development of a thermochemical reaction

which yields a portable chemical with a

high-energy density would also make “direct” solar transportation a possibility. It is

unlikely that the direct solar sources wouId

be preferred to synthetic fuels from biological or other sources.

Considerable caution must be exercised in

interpreting statements about the “competitiveness” of solar energy systems. First, the

benefits of solar equipment can only be

realized if the prospective owners compare

solar and alternative systems on the basis of

life-cycle costing. Life-cycle costs will, in

turn, depend on the type of owner since

each wilI have a different tax status, sources

of capital, and economic expectations.

Solar devices may be owned by the residents

of the building, a private corporation, or a

municipal or privately owned utility. Each

will make different estimates of the advantages of the solar investment. Whether prospective solar customers will actually employ such a procedure is difficult to anticipate and will depend to some extent on the

skill with which the solar equipment is sold.

It is difficult to establish a fair basis for

computing the cost of nonsolar equipment

since the performance of nonsolar equipment is Iikely to improve as the price of conventional energy increases. There is also

great variation in the cost of energy around

the country; regional differences in energy

prices are greater than differences in the

amount of sunlight avaiIable.

it must be recognized that if onsite solar

energy is to make a major impact on the U.S.

energy economy by the turn of the century,

it will be necessary to find ways of instalIing

solar equipment on existing buildings. This

process can be difficult: such installations

are likely to be more expensive than devices

attached to new structures, although there is

at present no reliable information about the

additional costs which could be expected. It

is Iikely that the percentage increase in costs

would be smalIer in larger buiIdings,
22 ● Solar Technology to Today’s Energy Needs

There may well be situations where it is

not possible to retrofit an existing structure

with solar equipment. Densely populated urban areas and heavily treed suburbs present

particularly difficult problems, and solar

energy used at these sites is unlikely to

come from onsite systems. Building orientation may present difficulties in some cases

but a roof must have a particularly poor

orientation or roof shape to present a major

problem for a solar installation.

POSSIBLE IMPACTS OF ONSITE SOLAR ENERGY

Since onsite solar equipment would undoubtedly be designed, manufactured, financed, installed, and operated by the same

organizations currently associated with the

construction of buildings and industrial

facilities, the impact on American society as

a whole will probably be very minimal. Several areas, where impacts would probably

be greatest, have been identified and

studied in some detail.

U.S. SECURITY AND WORLD TRADE

Extensive worldwide development of solar energy systems would, in time, relieve

some of the strain imposed on international

stability by competition for energ y

resources, reducing economic difficulties

faced by oil-importing nations. It could provide a reliable source of power not dependent upon imports, and the necessary technology would be accessible without a need

for large numbers of highly trained engineers or foreign technicians to operate

them. It should be possible for many countries to manufacture solar equipment using

existing industrial and construction skills

and facilities. Solar energy will be economicalIy attractive i n most other countries before it is competitive in the United States

where energy is relatively plentiful and inexpensive. The development of indigenous

energy sources abroad should also reduce

pressures to accelerate the development of

nuclear power, thereby reducing opportunities for the proliferation of the technology

and materials required to make nuclear

weapons.

I n spite of the development of indigenous

solar industries abroad, foreign markets for

solar energy devices may provide an excellent opportunity for U. S. exports, Since

many nations will find it desirable and possible to manufacture solar equipment locally,

the sale of licenses, patents, and turn-key

plants may dominate exports. The international utilization and impact of solar energy, however, may depend critically on U.S.

initiatives over the next few years. I n most

areas, U.S. research is the most advanced in

the world, so many nations will look to the

United States for guidance in this field. A

U.S. commitment to solar power would encourage foreign commercialization of the

technology, if only by giving it prestige.

LABOR

Onsite solar technology appears to be

more labor-intensive than contemporary

techniques for supplying energy, thus, in the

short term, the introduction of solar energy

devices will create jobs in trades now suffering from serious unemployment. Jobs would

also be created by replacing imported oil

and gas with solar energy derived from domestically produced equipment. Jobs would

be created in the following areas:

●

●

Manufacturing of components (solar

collectors, heat engines, photovoltaic

devices, storage batteries, controls,

etc.),

Installation of systems (plumbing,

sheet-metal work, steamfitting, electrical work, carpentry, excavation, and

grading), and
Ch. I Introduction ● 2 3

●

The

Maintenance of installed systems (including routine adjustments and repairs

for small systems and full-time operators for larger units).

work created in these areas will be

distributed widely across the country, allowing most workers to find jobs in areas close

to their homes, and the jobs created should

be relatively safe. One effect of emphasizing onsite solar energy, for example, would

be to create more new construction jobs

than new coal-mining jobs. It is also interesting to notice that nearly a third of the

employment associated with a conventional

electric utiIity involves transmission and

distribution of energy and billing and other

services — services which would probably

not be affected in any way by a shift to onsite power. There would be no need for

laborers to live in remote or temporary construction sites. Work on solar equipment

shouId require onIy simple retraining programs for most construction trades. There

may, however, be shortages both of engineers and architects qualified to design

solar equipment, and of operators trained in

the maintenance of some of the larger and

more sophisticated solar devices that have

been proposed.

The long-term applications for employment of solar and other new energy technologies cannot be reliably assessed with contemporary economic methods. Long-term

labor impacts will depend on forecasts of

future growth rates, both in the economy

and in U.S. energy consumption — subjects

about which there is great confusion and

disagreement.

UTILITY PARTICIPATION

Utility participation in onsite generating

facilities offers several advantages:

● The utiiity is i n the best position to optimize the size and placement of all

generating, storage, and transmission

equipment in the region;

●

●

●

Utilities alone can compare the cost of

energy from new onsite equipment with

the cost of energy from new central facilities — al I other owners wilI compare

onsite costs with the lower, average

cost of energy from all central generating faciIities;

Utilities can offer the equivalent of 100

percent financing for new generating

plants (onsite or otherwise) and are able

to raise capital for investments with

long-term paybacks–something which

few other institutions can do; and

Utilities already have maintenance

crews and billing services, which could

be expanded to cover the operation of

onsite generating equipment.

A number of these advantages could be realized without utiIity ownership of onsite systems if care is taken in the design of utility

rates.

Municipal utilities may be able to play an

important role in regional planning for onsite solar energy systems and their access to

relatively low-cost capital may make municipal financing of solar energy projects attractive.

ENVIRONMENT AND LAND USE

While solar energy equipment is not completely free of adverse environmental effects, providing energy from sunlight will

have a much smaller environmental impact

than conventional sources providing equivaIent amounts of energy.

Solar energy may provide an opportunity

to expand population and increase industrial capacity in areas where such growth

may be constrained by the Clean Air Act.

Large-scale conversion to the direct combustion of coal wiII make it difficuIt to maintain

current levels of air quality unless solar

energy, or some other nonpolluting energy

source, is introduced to reduce the demand

for energy from fossil sources. The use of

solar energy can also reduce the net releases
24 ● Solar Technology to Today’s Energy Need s

of carbon dioxide. The significance of this

depends on the extent to which greatly increased CO2 releases could adversely affect

world climates— and this is not well understood now.

The primary environmental effect of utilizing onsite solar energy will be reduction of

the potential adverse environmental effects

associated with other energy sources. The

negative environmental effects of solar

energy devices stem primarily from two

sources: (1) land-use requirements, which

could compete with other, more attractive

uses of land near populated areas, and (2)

emissions associated with the mining and

manufacture of the materials used to manufacture solar equipment (e. g., manufactured

steel, glass, aluminum, etc. ) In most of the

cases examined, however, the reduction in

emissions attributable to operating a solar

facility instead of a conventional one can

FEDERAL

One of the attractive features of onsite

solar equipment is that it may be the only

new energy source that can be developed, financed, and installed without Federal assistance of any kind; it is simply an extension of

existing construction industries. Federal

energy policy will, however, affect the rate

at which onsite solar energy enters the market, regardless of whether an attempt is

made to develop a specific policy for solar

energy. Federal poticies have made the market in which solar technologies compete an

artificial one. Energy prices are influenced

by a bewildering array of regulations, subsidies, and controls which, in several instances, have had the inadvertent effect of

reducing the attractiveness of solar equipment. Examples include the policy of maintaining residential energy rates at artificially

low levels, decisions to support larger types

of energy equipment with preferential tax

credits, and disproportionate amounts of

research funding given to larger energy

equipment.

equal the extra emissions associated with

the manufacture of the solar device in 3 to 9

months. In addition to these primary effects,

a number of the specific storage and energy

conversion systems discussed in later sections of this report could have adverse environmental effects because of noise, minor

emissions (associated primarily with manufacturing components), and use of toxic

chemicals.

The land-use impact of onsite solar equipment can be less serious than the problems

associated with isolated solar equipment,

since in most cases the onsite equipment

can be integrated into buildings or local

landscapes and extensive transmission facilities are not required. If additional surface

area is required, however, lack of suitable

land close to populated areas could place

major constraints on the use of onsite solar

equipment.

POLICY

There is little doubt that without Federal

assistance, solar markets wilI grow relatively

slowly. Legislation can greatly accelerate

the rate at which this market grows if this is

judged to be a desirable objective.

The following types of policies can be effective.

1. Direct incentives to potential customers (chiefly tax incentives, loan subsidies, and allowances of accelerated depreciation).

2. Assistance to manufacturers (including

3

incentives for purchase of manufacturing equipment, research and development grants, and Federal purchases)

and assistance for testing laboratories

certifying the performance of onsite

equipment.

Support of basic research and development programs in fields related to onsite solar energy.
Ch. I Introduction ● 2 5

4

5.

6.

Legislation which might eliminate some

barriers to usage of onsite solar systems

(this would include freeing onsit e

equipment from regulation as a public

utility and assisting States in designing

local procedures for protecting the

“sun rights” of owners of solar equipment).

Encouragement of the use of solar energy in other countries through foreign

assistance grants, joint research programs, and other techniques.

Programs to support education and

training in fields related to solar energy.

Tax credits, low interest loans, accelerated depreciation alIowances, and exemption from property tax can be powerful tools

in reducing the perceived cost of solar

energy. A 20-percent investment tax credit,

for example, could reduce the effective cost

of solar energy in residential applications by

15 to 30 percent; the combination of a 20-

percent investment tax credit; 5-year depreciation alIowance, and an exemption from

property tax, could lower the perceived cost

of solar energy by 50 to 80 percent. A program making 3-percent loans available to

homeowners would be equivalent to an investment tax credit of about 34 percent.

These subsidies would have the effect of increasing sales, resulting therefore in a

decrease in the cost of individual components if they stimulate mass production.

Tax credits reduce Federal revenues but

the net cost of the credits to the Government is difficult to calculate, The Federal

subsidy per unit of energy produced by subsidized solar equipment is roughly equal to

the difference between the costs (with or

without incentives) of a unit of solar energy

perceived by equipment owners. That is, if a

policy has the net effect of reducing the

customer’s perceived costs by $0.01/kWh,

the Government will lose approximately

$0.01/kWh in tax revenues for each kWh

generated by the solar system receiving the

subsidy. The Government’s costs, however,

will be compensated to some extent by the

fact that solar-related businesses would be

stimulated by the subsidy, thus producing

increased tax revenues. This analysis of

costs does not attempt to attach a monetary

value to the health benefits of reduced air

polIution and other social benefits

Federal support of small solar energy systems has been consistently hampered by the

small staff available to DOE’s Division of

Solar Energy Small staffs make it difficult

to manage a large number of innovative

projects.

STANDARDS

A difficulty encountered with any new

technology, and particularly one involving

as many small and inexperienced manufacturers as in the current solar energy industry,

is that it is necessary that standard testing

procedures be developed rapidly, and in

step with the development of each type of

technology. It is also necessary, however,

that these standards be reviewed constantly

so that new and different design approaches

are not inadvertently ruled unacceptable.

Small firms are frequently in such a weak

financial position that it is difficult for them

to offer acceptable guarantees. A reputation for failed installations could be a

serious barrier to the rapid expansion of the

solar industry,

Standards have been slow to develop and

inspectors frequently do not know what to

look for in novel systems.

OTHER SPECIALIZED LEGAL AND

REGULATORY PROBLEMS

Onsite solar facilities are currently controlled by laws and regulations written with

entirely different energy systems in mind.

Although that is the case, this study finds

surprisingly few barriers to large-scale instalIation and operation of onsite solar facilities. The legal barriers which do exist can, in

most cases, be removed with routine regulatory review. Resistance to changes in zoning
26 ● Solar Technology to Today’s Energy Needs

or building codes, for example, generally

arise when an interested party will be adversely affected; it is not Iikely, however,

that builders, owners, labor unions, or public officials will perceive onsite solar generation as a threat.

Some concern has been expressed about

the fact that owners of solar facilities have

no legal grounds for objecting to construction projects which would have the effect of

shading their collectors. While this may present a serious problem, the skillful application of existing legislation, local covenants,

zoning authorities, and buiIding code regulations will probably provide as much protection as it is reasonable to expect. The

analysis conducted for this study found no

need for Federal action in this area.

The regulatory problems which may present the greatest problems for onsite solar

energy devices, and the ones which it may

be most difficult to resolve, involve the laws

and rulings governing public investor-owned

gas and electric utilities. If it becomes possible to generate energy at competitive prices

using onsite solar energy equipment, the

“natural monopoly” of utility generation of

electricity, which forms the basis of most

utility law, would be called into question;

the only real “natural monopoly” may be

equipment for transmitting and distribution

of energy.

Problems in this area fall primarily into

three categories: 1 ) establishing just rates for

power sold as backup power for onsite solar

instalIations and just rates for utility purchases from onsite faciIities, 2) resolving the

regulatory problems faced when an individual or institution other than a utility attempts to sell electricity or thermal energy

(utilities are given a monopoly on such sales

in many regions), and 3) resolving the regulatory problems confronted when existing utilities attempt to own and operate onsite

energy equipment. Resolving these issues requires a clear concensus about the proper

role of utiIities in onsite equipment.

COMPARISON WITH CURRENT POLICY

This report does not make prescriptive

recommendations, but presents three points

of view which give rise to a range of specific

poticies affecting onsite solar power generation. The discussion (which appears in chapter I I I of this report) is intended to illustrate

the policy alternatives available and to

assess their relative effectiveness. This analysis found several broad approaches to be

potentially effective which do not play a significant role in current Federal programs. As

a consequence, the emphasis of this report

differs in several significant respects from

Administration policy.

1.

2.

3.

4.

The policies examined here would

place greater emphasis on accelerating

a wide variety of onsite solar energy

systems (including solar electric systems) during the next decade; the existing program appears to stress heating

and cooling systems, relegating most

other applications of solar power to

longer-term research programs and

placing major emphasis on the development of large, centralized electric-generating systems.

The policies examined here place a high

priority on bringing life-cycle costing

techniques to the attention of consumers, investors, and other groups in a

position to make decisions about energy equipment.

In contrast to the Administration’s plan,

which concentrates exclusively on consumer incentives, the policies examined

here will include a number of techniques for providing direct assistance

to equipment manufacturers.

Policies examined here place major emphasis on the problem of ensuring an

equitable relationship between onsite

solar equipment and existing utilities,

with particular emphasis on establishing reasonable rates both for the purchase of backup power from the utility

and for the sale of power generated by

onsite equipment to utilities. More at-
Ch. I Introduction ● 2 7

5.

tention is paid to providing backup

from natural gas and chemical fuels

rather than electricity and more attention is paid to the opportunities for

distributing thermal energy.

Policies here emphasize the encouragement of foreign sales of onsite generating equipment, licenses, and patents

and of providing assistance to nations

attempting to acquire a reliable, indigenous source of power.

Onsite solar energy has unique features as

an energy source, so Federal policy must

have unique features to encourage its development. Unfortunately, precedents for Federal programs, which have succeeded in encouraging the development of a commercial

product, are almost impossible to find; products developed and promoted by agricultural extension services are perhaps the only

clear exception. BadIy managed Federal intervention in the market can do more harm

than good. At a minimum, it must be recognized that developing and promoting a diverse set of technologies to be manufactured, installed, financed, and owned by a

diverse set of institutions will be very different from the programs designed to develop new central generating plants which will

clearly be designed for use and operation by

utiIities.

What will be needed is an unprecedented

amount of bureaucratic flexibility, imagination, and care in determining where Federal

intervention can help and where the best

policy is restraint.

There will be no way to avoid taking risks.

The bulk of this report attempts to provide

the basis for comparing the risks associated

with onsite solar energy equipment with the

risks which must be taken in supporting

other energy sources. If nothing else, the

study indicates that the potential of onsite

solar energy systems cannot be easily dismissed and that it is dangerous to be dogmatic about the subject at this early stage.

There is enough uncertainty about the future of the world’s energy supplies, and

enough problems have developed with conventional solutions, that it is necessary to be

a little humble about the extent to which

fundamental questions about supplying and

consuming energy are understood.
Chapter II

OVERVIEW OF ONSITE SOLAR

Technology AND SUMMARY OF

ECONOMIC ANALYSIS
Chapter II.--OVERVIEW OF ONSITE SOLAR TECHNOLOGY

AND SUMMARY OF ECONOMIC ANALYSIS

Page

Introduction em. ... .,*, *. ... ... ... ** 31

Methodology 8 - 9 . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2

Summary of System Costs for

conventional Buiidings ● . . . . ● . . . . . . . ● ..34

Technology Overview ● .*,**...,.....**.,,. . 36

Passive Solar Energy Systems . . . . . . .......36

Active Solar Systems . . . . . . . . . . . . . . . . . . . . 36

Summary of Cost Comparisons. . . . . . . . . . . . . . 40

Solar Heating and Hot Water . . . . . . . . . . . . ..40

Solar Air-Conditioning . . . ● * ● . . ● ..........43

Solar Electric Systems Using Photovoitaics .43

Solar Electric Systems Using Heat Engines.. 48

Community Energy Systems .. . . . . .. ......46

Industrial Systems . . . . . . . . . . .. . .. .......50

LIST OF TABLES

Table No. Page

1. Assumed Residential Fossil Fuel

Prices In the Year 2000 .. . ......... ......33

2. Typical Assumed Nonsolar Electricity Rates

in the Year 2000 . . . . . . . . . . . . . . . . . . . . . . . . 33

3. Levelized Monthly Energy Costs for Single

Family Houses Not Using Solar Energy ....35

4. Levelized Monthly Energy Costs for Single

Family Houses With Extra insulation .. ....35

Table No. Page

5 Levelized Monthly Energy Costs Per Unit -

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18

in a 196-Unit High Rise Apartment. . . . . . . . . 35

Levelized Monthly Energy Costs for Solar

Heating and Hot Water Systems . . . . . . . . . . 41

Solar Heating and Hot Water Systems for

Single Family Houses Compared With

Conventional Systems Based on Oil

and Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Levelized Monthly Energy Costs for Solar

Air-Conditioning and Heating .... ...... ..43

Fiat-Plate Photovoitaic Systems on

Houses With Extra insulation and Storm

Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Flat= Plate Photovoltaic Systems Mounted

on the Roof and Over the Parking Lot of a

196-Unit High Rise Apartment . . . . . . . . . . . . 45

Photovoitaic Concentrator Systems on

High Rise Apartments . . . . . . . . . . . . . . .. ...46

Heat-Engine Systems . . . . . . . . . . . . . . . . . . . 47

Buildings in the Community of 30,000.....46

Levelized Monthly Energy Costs Per Unit

for a Community in Albuquerque, N. Mex.. ..49

Levelized Monthly Energy Costs Per Unit

for a Community in Omaha, Nebr. . . . . . . . . . 50

Assumed Conventional Energy Costs for

Large industrial Users, 1976 Dollars . . . . . . . 51

industrial Direct Heat Systems Levelized

Monthly Cost . . . . . . . . . . . . . . . . . . . . . . . . . .52

industrial Cogeneration Systems Levelized

Monthty Cost . . . . . . . . . . . . . . . . . . . . . . . . . .54
Chapter II

Overview of Onsite Solar Technology

and Summary of Economic Analysis

INTRODUCTION

This study examines the cost and performance of a cross-section of onsite solar energy systems designed to meet all or part of the energy requirements of five different categories of energy customers:

—A two-story, single family, detached house with approximately 1,700

square feet of Iiving area.

—A 10-story, 196-unit, high rise apartment building.

—A shopping mall with approximately 300,000 square feet of commercial

space.

—A residential community consisting of a mixture of single family

houses, townhouses, low rise and high rise apartments, and commercial facilities.

—A series of industrial installations requiring differing amounts of process heat and electricity.

The systems were examined in four U.S.

cities— Albuquerque, Boston, Ft. Worth, and

Omaha– chosen to represent a range of different climatic conditions (both in terms of

the availability of the solar resource and the

heating and cooling demands). The cities

also represent a spectrum of different electricity and fossil fuel costs; this was important since the cost of energy from conventional sources around the country tended to

show greater variation than the amount of

available sunlight. The results presented in

this chapter are Iimited to an analysis of the

costs of hypothetical systems operating in

Albuquerque and Omaha.

The technologies chosen for analysis include devices which supply:

– Hot water for domestic or industrial

use;

– High-temperature fluids for industrialprocess heat;

– Hot water and space-heating;

— Hot water, space-heating, and air-conditioning;

– Electricity (from solar cells or heat

engines); and

— Electricity and thermal energy (using

total energy or cogeneration systems).

It was not possible to review the performance of all possible systems for onsite

systems designed to meet onsite energy

needs with direct solar energy, and it was

not possible to optimize the performance of

the systems selected. The analysis presented

here is intended only to establish the credibility of different proposals and to make

broad comparisons between competing concepts.

This chapter only summarizes the results

of the anaIysis; a much more compIete

assessment of the technologies represented

is reported in chapters VII l-Xl I of thi s

volume. Volume I I presents a much more

detailed review of the assumptions made in

the study, the methodology employed, and

reports the results of analysis of a much

larger number of cases than can be summarized here.

.31
32 ● S0lar Technology to Today’s Energy Need s

METHODOLOGY

WhiIe the cost of different energy sources

can be compared in a number of different

ways, the comparisons presented here were

all made by computing the average monthly

bill paid by the ultimate consumer of the

energy. This consumer might be the owner

of a single family house, a tenant in a high

rise apartment, or an individual purchasing

a product or service from a commercial or

manufacturing facility. These calculations

were made as follows:

1. Systems were compared on the basis of

2

their ability to meet the same set of

final or “end-use” demands for energy.

In the case of a single family house, for

example, this means providing energy

for domestic hot water, space-conditioning, and electricity for motors and

other miscelIaneous uses. If the solar

energy equipment was unable to meet

the demand (or was not designed to

meet some of the demands), these energy needs were met by using electricity

or fossil fuels from conventional

sources. The biIIing for this conventional energy was made on the basis of

actual rates currently charged in the

region.

All comparisons were made on the

basis of “life-cycle” costing methods.

This required an estimate of all outlays

for operating and maintaining equipment, electricity and fuels purchased,

taxes, and major replacements over a

selected 30-year period (1 985-201 5), as

well as an estimate of the initial cost of

the system. Estimates of the electricity

and fuel required by the different system designs were obtained by using a

computer model capable of calculating

the energy needed by each building

type for each hour of the year (described in detail in volume I I). When

solar devices were used, the computer

model also provided hourly estimates

of the amount of solar energy available.

The analysis was based on weather data

3.

taken in the four cities in 1962 (1963 for

Boston).

An accurate estimate of Iifecycle

costs cannot be made by simply adding

up all of the outlays made during the

30-year interval chosen for comparison.

A dollar spent in the 30th year will not

be as important to the owner of the system as a dollar spent during the first

year of the system’s operation —since,

in principle, the payment required in

the 30th year could be met in the first

year of operation by investing an

amount much smaller than a dolIar in

an account earning compound interest.

Cost comparisons were therefore made

by comparing the “present value” of all

expenditures, where present value is defined to be the amount which, if invested at interest in the first year of a

system’s operation, would be able to

meet all cash requirements for energy

(including the initial cost of the system).

Since each owner will have access to

different types of investments, a different effective interest rate must be

used to compute the present value of

outlays for each owner.

It was assumed that consumers compare costs on the basis of the “present

value” of their energy-related payments

and expect to earn a 10-percent return

(after taxes) on all investments. Payments consumers made were estimated

by computing the charges which would

be levied assuming the utilities or apartment building owners earned the same

rate of return on their energy investments that they earn on other types of

investments.

Using this method of comparing consumer costs, of course, does not imply

that consumers will actually select

energy equipment on the basis of such

a sophisticated financial analysis. Purchasing decisions are Iikely to be heav-
Ch. II Overview of Onsite Solar Technology 33

iIy infIuenced by first costs, the customer’s estimate of a system’s reliability

and convenience, and the skill with

which the item is marketed. No attempt

was made, therefore, to anticipate actual consumer behavior. The present

value technique is, however, the most

accurate technique available for evaluating the real cost of energy, and it

could be used to market energy-related

equipment in the future. The major

uncertainty in the method is the choice

of the consumer’s expected return on

investments,

4. All systems for meeting the fixed set of

end uses were compared as integrated

systems. This meant, for example, that

the performance of solar collectors and

the heating and cooling demands of

energy required to meet the heating

and cooling needs of buildings were

computed on an hourly basis assuming

that the buildings were operating in a

realistic set of climatic conditions.

While computing the cost of many types

of solar energy systems is treacherous because of differing estimates of the cost and

performance of solar equipment which may

become available in the next decade, it also

is extremely difficult to establish the cost of

conventional energy systems which may be

Table 11-1.—Assumed Residential Fossil Fuel

Prices in the Year 2000

(1976 $/kWhJ

Projec- Projec- Projection (l)* tion (2) tion (3)

Natural gas

Albuquerque. . . . . . . . . . . 0.0050 0.011 0.016

Boston. ... , . . . . . . . . . . . 0.011 0.024 0.036

Ft. Worth. . . . . . . . . . . . . . 0.0050 0.011 0.016

Omaha. . . . . . . . . . . . . . . . 0.0037 0.0082 0.012

#2 Heating oil

Albuquerque. . . . . . . . . . . 0.010 0.014 0.033

Boston. . . . . . . . . . . . . . 0.010 0.015 0.034

Ft. Worth. . . . . . . . . . . . . N,A. N.A. N.A.

Omaha. . . . . . . . . . . . . . . . 0.0096 0.013 0.031

. Actual 1976 rates N A = not available

NOTE A fuel prfce of $001/kWh corresponds to an average monthly fuel

b(ll of about $40/month for a single family house In Albuquerque

using fuel for hot water and heat!ng

operating during the next few decades. The

price of electricity, oil, and gas from conventional sources may change rapidly during the next few years, and the performance

of equipment designed to consume energy

from these sources may change dramatically as a result. Estimates of the future price of

oil, gas, and electricity vary greatly. And no

estimate is certain because of such imponderable as the rate of future oil discoveries here and abroad, the stringency of environmental controls, and political decisions made by international energy suppliers. Given the uncertainties about such a

critical variable, it was necessary to compare costs using several different forecasts.

The three forecasts used for most of the

comparisons in this paper are summarized

in tables I l-l and 11-2. They include assumptions that:

–The cost of electricity and fossil fuels

will increase at the pace of general inflation (5. s percent in this analysis).

(This is called “projection (1 ).”)

Table n-2.-Typical Assumed Nonsolar

Electricity Rates in the Year 2000

(1976 $/kWhe)

Projec- Projec- Projection (1)* tion (2) tion (3)

Albuquerque

SF . . . . . . . . . . . . . . . . . . . .0244 .0354 .0802

HR/SC . . . . . . . . . . . . . . . . .0207 .0300 .0680

Boston

SF . . . . . . . . . . . . . . . . . . . .0440 .0638 .1445

HR/SC . . . . . . . . . . . . . . . . .0557 .0808 .1830

Ft. Worth

SF . . . . . . . . . . . . . . . . . . . .0269 ,0390 .0884

HR/SC . . . . . . . . . . . . . . . . .0294 .0426 .0966

Omaha

SF . . . . . . . . . . . . . . . . . . . .0248 .0360 .0815

HR/SC . . . . . . . . . . . . . . . . .0217 .0315 .0713

.Actual 1976 rates.

NOTES These average values are representative of the more elaborate

electric rates! rUCl ure aClual!y used In the computer mode)

The model used actual utdlty rates In the region Includlng de.

mand charges and decllnlng block rates when these features applied In the region

SF = prices charged for single family houses using electric

heating

HR/SC = average rates charged for h(gh rwe apartments and

shopping centers Demand charges are Included, based on the

estimated peak demands of the bu( Idtngs In each city

An electricity price of $0 02/kWh corresponds to an average electrlc bill of about $70/month for an all electrlc house In Albuquerque
34 . Solar Technology to Today’s Energy Needs

– Energy prices wilI rise at rates predicted —Energy prices will increase by a factor

by a Brookhaven National Laboratory of 3.4 by the year 2000. Under this as-

(BNL) study. Electricity prices are ex- sumption, the price of oil and gas in

pected to rise by about 41 percent (in most cities would be roughly equal to

constant dollars) by the year 2000 (to the price of synthetic fuels. Electricity

roughly the current marginal cost of rates would increase to $0.07 to $0.10/-

electricity from new plants) and gas kWh in all cities examined except

prices to increase by 123 percent during Boston, where the price wouId be somethe same interval. (This is called “pro- what higher. *

jection (2).”)

SUMMARY OF SYSTEM COSTS FOR CONVENTIONAL BUILDINGS

The increases in energy prices already experienced, and anticipation of further increases, have accelerated the development

of efficient energy-consuming equipment. I n

almost all of the cases examined, investments in these energy-conserving devices

were more profitable than investments in

solar energy equipment, and it is always

preferable to make a careful assessment of

options for conserving energy before designing solar equipment for a building. Careful

control of energy consumption will, of

course, reduce the cost of the solar equipment required to meet the remaining load.

The cost of providing energy to single

family homes in Albuquerque and Omaha

which use different kinds of energy equipment are compared in tables I I-3 and I I-4. In

all cases, the costs were computed for the

years 1985-2015. (Most of the original equipment is replaced during this period, some of

it twice; all of these replacement costs are

evaluated in the analysis. ) The numbers

shown in the tables are the “levelized present value” of monthly energy bills. This

“levelized” payment is defined to be the

monthly payment which, if made regularly

for 30 years, would result in the same present value, from the customer’s perspective,

as the actual expenditures. The actual expenditures will, of course, vary from year to

year. The average monthly payments were

displayed because most consumers find estimates of monthly energy payments easier to

grasp intuitively. It should be noticed, however, that the average payments are some

what above those now made in the cities involved, since the levelized costs shown reflect inflation occurring during the period

when the system is operating.

Table II-3 shows the Ievelized monthly

energy payments for houses equipped with

several different kinds of gas furnaces, electric heaters, and heat pumps now on the

market. The table also indicates the payments which would result if the performance of the equipment is improved. Oil and

gas furnace efficiencies can be increased

with careful design of the burners and by

reducing flue temperatures. Hot-water heaters can be made more efficient by adding insulation. The table shows that investments

in these improvements are attractive, even if

the price of energy remains at 1976 levels

(projection (1 )).

While the heat-pump systems are less expensive to operate than electric-resistance

systems, the benefits of the energy-saving,

heat-pump systems are smaller than expected when a careful life-cycle cost analysis is used. This is because the heat pumps

are more expensive to purchase initialIy and

the expensive compressor elements of heat

pumps typicaliy are replaced every 8 to 10

years. (Analysis in chapter V shows that the

comparisons are even less favorable to heat

pumps when the real cost of providing

power to baseboard and heat-pump systems

from conventional electric utilities is com-

‘All energy prices cited here and elsewhere In the

report are given In 1976 dol Iars
Ch. II Overview of Onsite Solar Technology 3 5

Table II-3.—Levelized Monthly Energy Costs for

Single Family Houses Not Using Solar Energy*

Energy projection* ● ●

Standard houses* ● (1) (2) (3)

Gas furnace, gas hot

water, central electric a/c

Gas furnace and hot

water with improved

efficiency, central electric a/c

Gas heat, hot water,

gas absorption a/c

Oil furnace and hot

water, central electric

a/c

Oil furnace and hot

water with improved

efficiency, central elec.

tric a/c

Baseboard-resistance

heat, electric hot

water, window a/c

Electric heat pump and

electric hot water

116 173 287

125 180 302

111 160 265

121 169 284

122 187 295

127 188 297

179 230 458

204 263 522

163 208 406

186 237 461

177 238 490

206 277 570

156 203 395

190 249 490

Improved electric heat A 146-162 187-203353-367

pump, electric hot water O 173 223 424

——.

“System operates from 1985.2015

+‘3 !iz.inch.fiberglass Insulation (n walls, 6 lnCheS In Celllng

“‘ “See table 11-1

A = Albuquerque O = Omaha

puted – the tables reflect electric rates now

charged in the regions. ) The performance of

heat pumps can be increased by developing

better compressors, using multiple compressors, and with other techniques. These improvements can make the heat pump systems more attractive if the cost of the improvements is low, A 50-percent improvement i n heat pump performance is economic if it increases heat pump cost by 20

percent, but may not be if the cost increase

is 80 percent.

Table I I-4 indicates the Ievelized monthly

costs which result from adding extra insulation and storm windows and doors to the

houses examined in table 11-3. It can be seen

that this investment is attractive even if

energy prices do not increase in real terms.

Table I I-4 also shows the costs which

could be expected from a system that provides all energy needs, including electricity,

by burning natural gas. This is a “totalenergy” system using a gas-fired heat pump

to provide heating and cooling; the engine

Table II-4.—Levelized Monthly Energy Costs for

Single Family Houses With Extra Insulation*

Energy price project ion ● ●

(1) (2) (3) With

20-percent

ITC on

energy conservation

equipment

Gas furnace, gas hot A 106 153 254

water, central electric a/c O 111 154 261

Oil furnace and hot A 153 195 380

water, central electric O 163 208 402

a/c

Baseboard-resistance A 149 198 399

heat, electric hot o 159 211 423

water, window a/c

Heat pump and A 142 183 350

electric hot water 0 161 208 399

Gas heat pump and on- A 113 146 173

site electric generator O 106 133 157

(using waste heat)

“System operates from 1985-2015 6-inch fiberglass Insulation !n walls, 12

Inches [n celling, storm windows, and doors

. ● See table 11-1

A = Albuquerque O . Omaha ITC = Investment tax credtt.

used to operate the heat pump compressor

is also used to generate electricity. Waste

heat from the engine’s cooling system is

used to supply hot water and supplement

the heating system. The cost of operating

such a system is expected to be very close to

the cost of operating an all-electric house.

Table 1 I-5 compares the Ievelized monthly

Table II-5.—Levelized Monthly Energy Costs Per

Unit in a 196-Unit High Rise Apartment*

Energy price projection* ●

(1) (2) (3) With

20-percent

ITC on

energy conservation

equipment

Gas heat, gas hot A 51 71 129

water, central electric a/c O 57 76 129

.System operates from 1985-2015 “ “See table 11-1

A = Albuquerque O . Omaha ITC = Investment tax credit
36 ● Solar Technology to Today’s Energy Needs

costs borne by the tenants of a high rise

apartment, assuming that all energy equipment was financed with the rest of the building. It is assumed that capital costs are simply included in the building rent. The advanced system shown in this case assumes

the use of a diesel engine, total-energy system, which provides all needed heating,

cooling, hot water, and electricity. Heat is

received from the engine by placing a boiler

in the exhaust of the diesel. Some of this

thermal energy is used to operate a lowtemperature heat engine when electric

demands are high.

TECHNOLOGY OVERVIEW

PASSIVE SOLAR ENERGY SYSTEMS

The techniques just described for conserving energy in buildings can be supplemented

by carefully designing buildings to: (1) maximize the amount of solar energy absorbed

during winter and (2) minimize the heat absorbed and maximize natural convective

cooling during the summer. Such techniques, which have come to be called “passive” solar systems, are principally skillful

architecture and landscaping; many of the

most attractive techniques were in widespread use in building designs before lowcost energy sources created a situation

where buildings were designed without attention to energy consumption.

Energy requirements can be reduced by

paying careful attention to the orientation

of a building on its lot, the location of trees,

the use of awnings or overhangs which permit sunlight to enter a room during the

winter but shade the window during the

summer cool ing season, and other basic

architectural features. Window size and

location are particularly important. Large

south-facing windows can provide over sO

percent of the heating requirements of a

room, even in climates with severe winters.

Some passive buildings have covered the

southern face of the house with a greenhouse. The performance of such systems

can be improved by using thick walls and

floors to store heat in the building’s interior

and by using movable insulation, such as

shutters which can be adjusted to reflect

outside heat or preserve heat in the building

interior as needed. Carefully designed interior ventilation can amplify the heating

and cooling available from such systems.

These systems may well be able to provide space-conditioning at a price comparable with or lower than the price of solar

energy from the active systems examined in

greater detail in the remainder of this

chapter. It is often difficult, however, to

determine the real incremental cost of passive solar equipment. (For example, how

does one account for the fact that the addition of a greenhouse may make a building a

more pleasant place to Iive?) While passive

systems are usually extremely simple, and

the principle of operation easily understood,

analysis of their performance is only beginning. This study did not attempt to perform

a detailed examination of these systems.

ACTIVE SOLAR SYSTEMS

A Survey of Components

Active solar systems require components

which are distinct from the basic building

structure. The systems consist of three basic

elements:

1 A solar collector exposed directly to

the Sun which converts light into a

heated fluid or, in the case of solar

cells, converts light directly into electricity.
Ch. II Overview of Onsite Solar Technology ● 3 7

2. An energy-storage system which stores

excess energy available during sunny

periods for use when direct sunlight is

not avaiIable.

3. An energy-conversion system which

converts the heated fluids into mechanical energy or electricity through a generator using a turbine or piston engine.

Not all solar systems will use storage or

energy-conversion equipment.

SOLAR COLLECTORS

The design of attractive, reliable, low-cost

collector systems is critical to the future of

solar energy since the bulk of the cost of

solar systems usually is attributable to the

collectors and they are often highly visible.

The collectors must cover areas large

enough to collect the solar energy required,

and these areas can be substantial since, at

its peak, sunlight provides only about 1 kilowatt (kW) per square meter. The actual output of a square meter of collector, however,

is much less than 1 kW. A typical photovoltaic coIIector can convert only about 10 percent of the incident sunlight energy into

electricity, and the average intensity of

sunlight (averaged over all hours of the

year – day and night) is typically about onefifth of the peak solar intensity. As a result,

about 50 square meters (540 square feet) of

these collectors (connected to an appropriate storage device) are needed to provide

a continuous kilowatt of solar electricity. (A

continuous kilowatt wouId keep ten 100-

watt light bulbs burning. ) Providing this continuous kilowatt, therefore, means that so

square meters of some kind of material must

be supported and made secure against adverse weather. Thermal collectors, used to

provide hot water for heating or other purposes, typically are 2 to 4 times as efficient

as the photovoltaic systems just described

and require a proportionally smalIer area to

provide a continuous kilowatt of thermal

output.

Two types of collectors are now on the

market: nontracking collectors and collectors that follow or track the Sun during the

day. Nontracking or flat-plate collectors

have no mirror surfaces or moving parts and

thus have the advantage of simplicity and

reliability. They can be integrated into most

architectural styles without being obtrusive.

Flat-plate systems can capture “diffuse”

sunlight (light reflected from the ground or

the clouds), which most focusing collector

systems cannot do.

Concentrating collectors that track the

Sun can generate much higher temperatures

than flat-plate collectors and therefore are

more valuable for systems that use heat

engines or for some types of industrial processes. They also can provide somewhat

more output than flat plates. Few tracking

collectors are now on the market, and most

are relatively expensive. The potential for

savings in production costs is large because

they can use thin reflecting surfaces or

plastic lenses over most of the area covered.

Whether the cost of maintaining the equipment required to keep them pointed toward

the Sun offsets the increased output is not

now known and cannot be determined without operating experience. Collector alternatives are discussed in greater detail in

chapter VII I.

SOLAR ELECTRIC SYSTEMS

EIectricity can be generated directly from

sunlight in two ways: (1) by heating fluids to

operate heat engines (such as steam turbines) that turn electric generators; and (2)

by using photovoltaic cells (solar cells) that

are solid-state devices made from the same

basic materials as transistors. Both approaches can be used to produce electricity

alone or to provide both electricity and heat

in a “total energy” or “cogeneration”

system.

Heat Engines

Heat engines operate by taking a hightemperature fluid (which may be steam or a

heated gas) and converting some of the

fluid’s energy into mechanical power or

electricity, cooling the fluid in the process.
38 . Solar Technology to Today’s Energy Needs

The fluid which emerges from the engines

can still be quite hot, however, and can be

used for space-heating or other applications.

A number of heat engine designs eventually may be used in solar installations, but

the small engines now on the market which

are compatible with solar energy applications are quite expensive. Small gas and

diesel engines cannot be easily used in solar

systems since they require heat applied inside a cylinder; most engines designed for

solar applications must be able to operate

from heat applied to some external surface

(e.g., to the boiler of a steam turbine).

Technology is available, however, for

designing engines capable of operating from

many different kinds of solar-heated fluids.

The most straightforward approach is to use

a solar coIIector to produce steam (typically

at temperatures between 4000 and 1,0000 F)

and use this steam in standard steam turbines or piston engines. The engineering of

large steam turbines (100 megawatt and

larger) is very advanced, and efficiencies

above 40 percent are possible with hightemperature steam. Much less work has

been done on smaller steam engines in recent years, however, and designs tend to be

somewhat archaic.

The use of steam, of course, means that a

high-performance tracking-collector system

must be used, and a storage device must be

developed which is capable of holding hightemperature thermal energy. It is possible to

use much simpler collectors and storage devices with engines designed to operate at

lower temperatures. Water is not a desirable

working fluid at temperatures below 4000 F

(and may not be desirable at temperatures

below about 8000 F). Engines analogous to

steam engines have been designed which are

able to operate from fluids at temperatures

as low as 1300 to 1800 F. These engines use

freons (similar to the fluid used in refrigerators) or other organic fluids instead of water.

The low-temperature systems can be extremely reliable (they are essentially refrigerators working backwards), but their efficiency is low (less than 10 percent if fIuids of

1500 F are used), and contemporary devices

tend to be bulky and expensive in small

sizes.

A number of heat-engine designs also are

available which are able to operate at the

opposite extreme of temperatures. Braytoncycle devices, similar to the gas turbines

used in aircraft engines, may be practical if

collectors can be developed which are capable of producing temperatures of 1,4000 For

more at reasonable cost. Such systems will

require the use of heliostat fields or other

two-axis collectors. Relatively little work has

been done on small, high-efficiency, Brayton-cycle devices, however, although several concepts are being pursued in connection with research on gas-powered heat

pumps.

Small engines based on the Stirling or the

Ericsson cycle may eventually prove to be

the most attractive devices if high temperatures are available. These engines may be

able to achieve efficiencies as high as 50 to

60 percent at relatively modest cost, but

much more development work is required

before reliable systems will appear on the

market, It is unlikely that any engines based

on these two cycles will be available commercially for several years, and they will be

quite expensive unless mass produced.

In addition to the systems just described,

a large variety of devices capable of converting thermal energy to electrical and mechanical power are in early stages of development. Chapter IX discusses engine cycles

in greater detail.

Photovoltaic Systems

Photovoltaic devices, similar to the “solar

cells” used to provide power for spacecraft,

can convert sunlight directly into electricity

with no moving parts. As a resuIt, they can

be extremely reliable and quiet. The cells

are not as efficient as the best heat engines,

but they can compete in efficiency with

heat engines at lower temperatures (i. e.,

4000 to 5000 F or lower). The main disadvantage of the photovoltaic technology at present is its extremely high cost. While inexpensive heat engines may cost as Iittle as $100
Ch. II Overview of Onsite Solar Technology . 3 9

to $200 per kilowatt, photovoltaic systems

currently selI for approximately $11,000 per

kilowatt. (The photovoltaic systems can provide this peak output only in bright sunlight, ) Current Federal research programs

have as their goal a cost for photovoltaic arrays of $2,000 per kilowatt by 1982 and $500

per kilowatt by 1986 (in 1975 dolIars). Photovoltaic systems are discussed in detail in

chapter X,

There are four basic approaches to

achieving a cost reduction for solar celIs:

1. Reducing the cost of manufacturing silicon celIs, which are the most common

photovoltaic devices This requires developing mass-production techniques

to replace the inefficient processes now

used to fabricate cell arrays, and it will

require developing inexpensive techniques for producing and slicing silicon

crystals. Silicon is an attractive material because it is plentiful and nontoxic.

2. Developing cells based on “thin films”

of materials, such as cadmium sulfide

or amorphous siIicon, which can be applied directly to glass or other supporting material at very low cost. The

main difficulty with the present thin

film cells is their relatively low efficiencies. Low efficiencies mean that relatively large areas are required, and the

cost of supporting these large areas of

cells may exceed the cost of the cells

themselves Competitive thin film cells

probably will require efficiencies greater than 10 percent.

3. Using concentrating collectors to focus

sunlight on photovoltaic cells, thereby

reducing the area of celIs required for a

given energy output. A number of cell

designs are being developed which are

able to operate in a wide range of solar

intensities. Some of these designs are

variants of siIicon designs, whiIe others

are based on galIium arsenide or other

materials, The use of concentrating collectors replaces the problem of reducing cell costs with the mechanical problem of designing a focusing collector

4.

which can be manufactured at low

cost. One feature of the concentrating

systems is that it may be economically

attractive to cool the cells with a fluid

and use the heated flu id for space-heating or other processes, thereby taking

maximum advantage of the investment

in the coIIector.

Using properly designed sheets of plastic or glass imbedded with a fluorescent

dye to concentrate sunlight reaching

the face of the sheet on the thin edge of

the sheet. (Anyone holding a sheet or

rod of clear plastic may have noticed

how the edge or end sometimes seems

to glow. ) The use of such a concentrator would eliminate the need to

develop a low-cost focusing and tracking system, but there would be a need

to find a low-cost dye with the proper

optical properties capable of surviving

bright sunlight for many years.

During the last few years, a number of

techniques have been proposed for using

photochemistry to generate hydrogen and

other chemicals directly in solar collectors

with chemical reactors driven by sunlight,

The chemicals produced could then be

stored or burned much like natural gas.

Several preliminary tests have demonstrated

the feasibility of the approach, although the

efficiency of current processes is quite low,

ENERGY STORAGE AND BACKUP

The real cost of solar energy technology

cannot be evaluated without considering

the cost of energy supplied when direct sunlight is not available. The optimum process

for maintaining energy availability depends

on the relationsip between onsite users and

existing utilities and on the eventual cost

and performance of various storage technologies. Three basic approaches are possible

for providing energy in an onsite solar system during periods when direct solar energy

is not avaiIable:

– Energy can be generated by using fuel

at an onsite faciIity.
40 . Solar Technology to Today’s Energy Needs

— Electricity can be purchased from electric utilities for backup (and possibly

sold to utilities when the output of onsite devices exceeds local demand).

— Energy can be stored in onsite storage

devices.

There are several approaches to storing

energy at a given site: fluids produced by

thermal colIectors can be stored directly, for

example, and electricity generated by onsite

systems can be stored in batteries or other

electrical storage systems. It may be desirable to transmit thermal energy, electricity,

or chemicals generated in onsite devices to

central or regional storage faciIities.

The lowest cost systems now available for

storing thermal energy at low temperatures

(below 2500 F) are simple hot water tanks or

bins of heated rocks. These systems are so

inexpensive that it will be difficult to find

competitive alternatives, Present storage

costs in such devices range from $0.50 to $5

per kilowatt-hour of capacity of the device.

Some advanced concepts for storing large

amounts of low-temperature energy in underground caverns, aquifers, or porous rock

could reduce this cost to $0.10 per kilowatthour or less, The somewhat lower efficiency

of these large storage systems partially offsets the advantage offered by their low initial cost.

The price advantage of low-temperature

storage may make it desirable to store energy during the summer for use during the

winter.

High-temperature thermal storage is more

expensive. Some types of oil can be used to

store energy at temperatures up to about

6000 F for $2 to $5 per kilowatt-hour. Storage at higher temperatures (1 ,4000 to 1,6000

F) costs $3o to $5o per kilowatt-hour.

Electric storage is another option. The

only electricity storage systems now commonly used by electric utilities employ hydroelectric facilities, in which water is

pumped into an elevated reservoir when demand is low and released to generate electricity when demand is high. Other storage

techniques in various stages of development

include advanced batteries, flywheels,

magnetic storage rings, and compressed air

in underground caverns. The only electricstorage systems which are Iikely to be compatible with onsite solar systems in the near

future will use some kind of battery.

The choice between storing energy and

providing backup energy from some other

source is very sensitive to the cost of storage

and fuels. I n many cases, it is more attractive to burn even an expensive fuel for a few

hundred hours during the year than it is to

provide all backup requirements from onsite

storage. Storage equipment is examined in

detail in chapter Xl, and the cost of different

kinds of backup is discussed in detail in

chapter V.

SUMMARY OF COST COMPARISONS

SOLAR HEATING AND HOT WATER

Although installations in four cities were

examined in detail, this chapter presents

only the results from Omaha and Albuquerque. Omaha was the least favorable location for solar energy systems of any of the

cities examined in the study because it

receives only average amounts of sunlight

and utility electricity and natural gas prices

there are relatively low. Albuquerque

receives nearly 40 percent more sunlight,

but, like Omaha, is below average in rates

charged for energy from nonsolar energy

sources. Moving from city to city, it is important to notice there is greater variation in

the price of electricity than in the amount of

sunlight available. Because of this, solar

energy is nearly as competitive in Boston

(where there is relatively little sunshine but

where energy prices are high) as in Albuquerque where the reverse is true.

Solar energy systems designed to provide

domestic hot water and space-heating require little more than a simple flat-plate col-
Ch. II Overview of Onsite Solar Technology . 41

Iector and a tank for storing the heated

water. Since it is often not desirable to run

tapwater through a collector, a “heat exchanger” is typicalIy used to transfer thermal energy from the collectors to the water

circulated to the house. Heat can be provided to the building interior by running the

solar-heated water through radiators or by

circulating the water through coils and

blowing air over these coils and subsequently through standard ductwork.

Table II-6 shows the Ievelized monthly

costs for solar systems designed to provide

building heating and hot water in Albuquerque and Omaha. (The cost range reflects different estimates of the future price of flatplate colIectors; the higher costs correspond

approximately to the price of some equipment which should soon be on the market

for new installations. Retrofits will probably

be more expensive )

The table also shows the percentage of

the building’s total energy requirements met

by solar energy. (Notice that this is not the

fraction of the heating or hot water load met

with solar energy, but the fraction of all

energy consumed for heating, hot water,

lighting, etc.) When electricity is displaced,

the primary energy consumed to produce

electricity from fossil fuels is computed.

It is clear that solar hot water systems

compare favorably with conventional electric systems in both cities, even in cases

where no increase in the real cost of energy

is assumed, Solar space-heating systems are

marginally competitive with the conventional heat-pump systems only if electricity

prices rise as forecast by the Brook haven

National Laboratory (BNL); they look extremely attractive if prices rise faster than

the BNL estimate. The solar devices would,

of course, appear more attractive in the case

of BNL price forecasts if investment tax

credits or other incentives are enacted.

Houses connected together with a thermal-piping system to a central “seasonalTable II-6.—Levelized Monthly Energy Costs for Solar Heating and Hot Water Systems*

Energy price projection ● ●

(2) With 20- (3) With 20-

percent ITC percent ITC

on solar on solar Percent

(1) (2) equipment equipment solar

Single family houses

House with electric heat pump and

electric hot water (shown for reference)

Solar hot water

Solar heat and hot water

Solar heat and hot water (300 houses

connected to central ‘‘seasonal”

thermal storage tank)

High rise apartments (cost per unit)

All-electric conventional systems

(shown for reference)

Solar hot water (all-electric backup)

Solar heat and hot water (all-electric

backup)

Solar heat and hot water with

seasonal thermal storage

156

190

141-147

184-191

158-187

201-227

165-214

215-299

83-84

83-87

84-87

85-89

87-95

91-104

57-85

92-127

203

249

176-182

234-241

184-213

245-271

184-234

237-321

112-113

109-113

110-114

109-113

113-120

111-123

69-97

103-137

203

249

174-179

232-237

177-201

237-260

171-211

217-285

395

490

316-321

437-442

284-309

416-438

249-290

307-375

112-113 229-232

109-113 215-223

109-112 218-220

107-110 203-206

109-115 212-218

105-114 186-196

66-84 116-134

90-114 134-157

0

0

28

17

48

29

65

76

0

0

19

13

31

26

53

61

.System operates 1985-2015 . “See table 11.1

A = Albuquerque O = Omaha ITC = Investment tax credit

28-842 0 - 4
42 . Solar Technology to Today’s Energy Needs

storage” facility can be provided with 100

percent of their heat and hot water demands

at prices not significantly higher than for

isolated solar systems on individual residences. In fact, the seasonal system is less

expensive in cases where energy prices are

expected to increase sharply.

Table I I-6 also indicates the costs of several heating and hot water systems designed

for use in a high rise apartment. The roof

area available on the building was not sufficient to support al I of the collectors required by the heating system examined; it

was necessary to erect racks over the parking lot for the building to provide the additional collector area required. Use of these

racks, of course, added to the cost of the

solar-heating system. It would be possible to

design a high rise building with much more

area for collectors, thereby reducing the

cost of solar energy. However, a conventional building design was chosen for analysis so that the costs estimated would apply

to a wider range of new and existing structures.

The table also shows the cost of systems

capable of providing 100 percent of the

heating and hot water needs of the high rise

building. In this case, there was no need to

connect several buiIdings to a common storage tank, since the tank for storing thermal

energy for the apartment was large enough

to achieve the required economies of scale.

The tank used in the analysis was assumed

to be a commercial steel or concrete tank

buried under the parking lot. (There is more

than enough room for such a tank under the

parking lot assumed for the building. )

Table I I-7 compares the cost of solarheating systems backed up with oil and gas

with the cost of conventionI energy sysTable n-7.-Solar Heating and Hot Water Systems for Single Family Houses

Compared With Conventional Systems Based on Oil and Gas*

Energy price projection ● ●

(2) With 20- (3) With 20-

percent ITC percent ITC

on solar on solar Percent

(1) (2) equipment equipment solar

Natural gas used as a backup

Albuquerque—

Conventional gas system . . . . . . . . . . . . .

Solar hot water system . . . . . . . . . . . . . . .

Solar heating and hot water system . . . .

Omaha—

Conventional gas system . . . . . . . . . . . . .

Solar hot water system . . . . . . . . . . . . . . .

Solar heating and hot water system . . . .

116

121-127

143-172

173 173

167-173 165-170

172-201 164-188

287

268-273

251-276

125

135-142

165-191

180 180

185-191 182-188

207-233 199-221

302

298-303

308-330

Heating oil used as a backup

Albuquerque—

Conventional oil heat . . . . . . . . . . . . . . . .

Solar hot water system . . . . . . . . . . . . . . .

Solar heating and hot water system

(45m2

) . . . . . . . . . . . . . . . . . . . . . . . . . . .

Omaha—

Conventional oil heat . . . . . . . . . . . . . . . .

Solar hot water system . . . . . . . . . . . . . . .

Solar heating and hot water system

(40m2

) . . . . . . . . . . . . . . . . . . . . . . . . . . .

179

168-173

230 230

210-216 207-212

458

392-396

0

18

165-194 193-222 185-209 302-326 45

204

202-209

263 263

254-261 252-257

522

480-486

219-244 262-288 255-277 444-466 26

“System operates 1985-2015. ● ● See table II-1. ITC = Investment tax credit.

NOTE: In all cases, solar systems are backed up with the fuel used by the conventional system used as a reference
Ch. II Overview of Onsite Solar Technology ● 4 3

terns using these fuels. In Albuquerque, the

solar devices will be competitive with both

oil and gas, if prices rise along the BNL

forecasts, and will be attractive in both

cities, if prices rise more rapidly. An increase

in gas prices which exceeds the price increases forecast by BN L is clearly possible.

SOLAR AIR-CONDITIONING

Three types of solar cooling were simulated with the computer model:

1. A solar-heated fluid can be used to

replace the burner in an absorption airconditioner simiIar to conventional airconditioners operated by burning

natural gas.

2. Solar-heated fluids can be used to

operate a heat engine connected to the

compressor of a standard air-conditioning unit

3. Photovoltaic devices can generate electricity which operates a conventional

electric air-conditioner.

Typically, the first two types of solarcooling systems require fluids at temperatures of 1800 to 3000 F and, as a result, require higher performance collectors than

solar heating and hot water systems.

Table II-8 compares the cost of several

different conventional and solar approaches

to air-conditioning. The results are somewhat difficult to interpret. Solar heating and

cooling systems backed up with gas compare favorably with conventional all-electric

systems, if BNL price projections are assumed. The solar systems compare favorably

with the all-gas conventional systems only if

a rapid increase in gas prices is assumed. An

investment tax credit for the solar systems,

however, could eliminate the cost differences in some locations.

SOLAR ELECTRIC SYSTEMS

USING PHOTOVOLTAICS

A simple photovoltaic system can consist

of an array of cells connected with an “inverter” capable of converting the direct current produced by the cells into the 60-cycle

alternating current which is compatible with

electricity provided by electric utilities. (It is

possible to use direct current for most lighting, electric stoves, electric heating, and

other purposes with Iittle or no modification

in the equipment –but a building would

need special wiring and switching to use

direct current, and this possibility will not be

examined in detail. ) Onsite storage can be

provided using batteries, but it is usually

preferable to sell excess electricity to the

electric utility rather than storing it onsite,

Utility storage tends to be less expensive,

and excess onsite energy is typically available during periods when there is a large demand for utility electricity and the excess

Table II-8.—Levelized Monthly Energy Costs for Solar Air-Conditioning and Heating*

Energy price projection ● ●

(2) With 20- (3) With 20-

(1) (2) percent ITC percent ITC

on solar on solar Percent

equipment equipment solar

Single family houses

“System operates 1985-2015 “ ‘See table II-1

A = Albuquerque O = Omah a ITC = Investment tax credit
44 ● Solar Technology to Today’s Energy Needs

onsite electricity is particularly valuable to

the utiIity.

As noted previously, a number of difficult

legal, regulatory, and rate-setting problems

will need to be overcome before onsite systems can be connected to utility grids in

most areas. (There should be no prohibitive

technical problems. ) For the purposes of this

chapter, it is assumed that electric utilities

purchase power from single family residences at exactly half the rate charged by

the utility for power and that utilities buy

power from high rise apartment systems at a

rate equal to 0.4 times the price the apartments pay for electricity.

Table I I-9 examines a number of flat-plate

photovoltaic devices which can be used on

the roof of a single family house. It is assumed that a weathertight roof exists under

the cell arrays, and that the roof needs no

special reinforcement for mounting the arrays. (The General Electric Company has

proposed using a photovoltaic array as a

shingle and argues that the devices should

be given a credit as a roofing material, but

no such assumption is used in the calculation presented in the table. ) It is assumed

that backup electricity is purchased at actual commercial rates (including demand

charges) and that utiIities are wilIing to purchase electricity in excess of onsite demands at a rate equal to 50 percent of the

price charged for electricity,

The analysis indicates that cells which

meet Department of Energy cost goals

($0.50 per peak watt) will be able to compete with conventional systems, if electricity prices increase slightly faster than the

Table ll-9.— Flat-Plate Photovoltaic Systems on Houses With

Extra Insulation and Storm Windows*

Energy price projection ● ●

(2) With 20- (3) With 20-

(1) (2) percent ITC percent ITC

on solar on solar

equipment equipment

Air-cooled silicon arrays ($0.50/watt) A 170 197 187 294 0 196 231 221 364

Air-cooled silicon arrays ($0.50/watt) A 190 215 202 303

and 20 kWh onsite batteries o 217 251 239 378

Air-cooled silicon arrays ($0.50/watt), A 157 177 164 182

and heat-engine backup o 161 178 165 182

(no electric connection)

29

32

38

37

46

37

90

75

100

80

“System operates 19852015 “ “See table II 1 tUse Improved heat pumps

A = Albuquerque O . Omaha ITC = Investment tax credit
Ch. II Overview of Onsite Solar Technology . 45

projection (2) forecast and some kind of investment tax credit is given to the solar

system; the solar systems would almost certainly be competitive with the marginal cost

of electricity produced from new plants.

The development of 10-percent efficient

thin-film arrays costing as little as $0.10 per

peak watt would result in systems able to

produce electricity at prices somewhat less

than the silicon systems. The savings are partially offset by the added cost incurred in

supporting and mounting the relatively large

arrays of thin-fiIm celIs.

Development of an efficient fluorescent

dye concentrator system would lead to very

significant savings, and systems based on

such designs would be able to provide a

large fraction of the total energy requirements of buildings with arrays covering the

southern roof. Such devices, of course, must

be considered extremely speculative at present.

One of the cases examined in table II-9

assumes that the house has no connection

to the electric utility grid. It has all of its

backup power supplied by a gas-fired heat

pump and generator. This system will be

competitive with the all-electric systems,

even if gas prices increase significantly faster than electricity prices.

Table I I-10 illustrates the cost of fIat-plate

systems used for apartment buildings. The

cost of the electricity from these systems is

somewhat higher than in the houses since

special racks need to be constructed for supporting the arrays over parking lots. This

places an added penalty on low-efficiency

systems requiring large collector areas. The

advantage of using the cells as a building

material, avoiding the cost of supports, is

clearly apparent by examining the next-toIast example shown in the table. In this instance, it is assumed that cells are used to

cover the southern wall of the apartments.

No credit is given for the weatherproofing

achieved by the arrays, but the cost of

mounting and installing the cells is not

charged as a solar-system cost. It can be

seen that this application is attractive even

though the cells are not mounted at an angle

which would maximize their output. The

building chosen for analysis again is not

well-suited to such applications, since its

southern wall can only accommodate cells

capable of providing 5 to 6 percent of the

total energy needs of the building.

Table 11-11 compares the cost of energy

from a variety of different photovoltaic systems mounted on concentrating, tracking arrays. It is assumed that the installed cost of

two-axis tracking devices is approximately

Table 11-10.—Flat-Plate Photovoltaic Systems Mounted on the Roof and

Over the Parking Lot of a 196-Unit High Rise Apartment ●
46 ● Solar Technology to Today’s Energy Needs

Table II.11 .—Photovoltaic Concentrator Systems on High Rise Apartments*

Energy price projection ● ●

(2)With 20- (3)With 20-

(1)

percent lTC percent lTC

(2) on solar on solar Percent

equipment equipment solar , ,

All-electric system (shown for

, ,

reference)

83-84

83-87

112-113

109-113

188

170

112-113

109-113

229-232

215-223

0

0

One-axis tracking unit with silicon

cells (near term)

164

154

164

147

261

213

63

41

120

125

Two-axis tracking unit with silicon

cells, cogeneration (near term)

114

113

214

178

37

42

Two-axis tracking unit with GaAs

cells (low cost)

85

99

100

104

153

108

Two-axis tracking unit with 40-

percent efficient cell

103

106

123

112

113

92

192

117

100

86

Two-axis tracking unit with 40-

percent efficient cell, diesel totalenergy system for backup

81

76

92

87

78

75

79

72

A

o

Two-axis tracking unit with GaAs

cells, 100-percent solar system with

seasonal electric storage (low-cost

iron-REDOX batteries) and no backup

114

218

114

218

92

176

92

176

100

100

● System operates 1985-2015. ● ● See table 11-1.

A = Albuquerque O = Omaha ITC = Investment tax credit.

$16/ft.2 The cogeneration systems are somewhat more attractive than the flat-plate

systems, even though the collectors are

more expensive, because a much higher net

efficiency is achieved from the collectors

(both thermal and electrical energy is produced). In cogeneration applications, the

very high efficiency celIs do not show major

advantages over the lower efficiency devices — they produce the wrong ratio of electric to thermal output for the building

chosen for study and excess electricity is

sold at a low rate.

price which may be possible, if the advanced iron-REDOX battery is developed.

It must also be recognized that the economics of the 100-percent solar system probably could be improved considerably, if

more care were taken to optimize the system —by examining the detailed tradeoffs

between collector sizes and the size of thermal and electrical storage devices installed.

Finally, the 100-percent solar systems require collector areas too large to fit on a

typical high rise parking lot.

Systems capable of providing electricity

and 100 percent of the heating and hot

water requirements of the building compare

favorably with conventional systems in several cases. The system designed to provide

100 percent of the building’s energy needs

from the solar equipment is competitive only if electricity prices increase relatively

rapidly. The 100-percent solar systems

shown here must be considered rather speculative, however, since it has been assumed

that electric storage costs only $11/kWh – a

SOLAR ELECTRIC SYSTEMS

USING HEAT ENGINES

Solar electric systems using heat engines

tend to be somewhat more complex than

photovoltaic systems and impose a more

difficult set of design decisions. The hightemperature fluids produced by the collector systems can be stored for later use in the

engine, the engines can have one or more

stages, heat can be extracted from the

engine at different temperatures to meet
.

Ch. II Overview of Onsite Solar Technology ● 4 7

direct heating requirements, and this relatively low-temperature energy can be stored

separately. The electricity produced by the

engine generator can be stored in batteries

or other onsite storage faciIities. Hydrocarbon fuels can be burned to operate the

engine when solar heat is not available.

Since it seemed unlikely that single family

homes would be equipped with high-temperature collectors or large tracking dishes,

the only heat-engine system examined for

these buildings involved the use of a oneaxis tracking system capable of producing

hot oil at 4000 F. Table II-12 indicates that

such a system could be attractive only if

electricity prices rise relatively rapidly.

Several more ambitious systems were examined for use with high rise apartments

and other building types. An organic Rankine-cycle system capable of meeting 100

percent of the energy requirements of the

building appears attractive only if thermalenergy storage is very low in cost (less than

$0.10/kWh) and electricity prices rise rapidTable ll-12.—Heat-Engine Systems*

Energy price projection* ●

(2) With 20- (3)With 20-

(1)

percent ITC percent ITC

(2) on solar on solar Percent

equipment equipment solar

Systems designed for use on a

well-insulated family house

House with gas heat, hot water, and

absorption air-conditioner (shown for

reference)

163

158

218

203

276

112-113

109-113

130-179

205-220

129

77

107

67

92

140

217

163

158

203

260

254

One-axis tracking system with 235

organic Rankine engine, lowtemperature thermal storage

only (Albuquerque)

One-axis tracking system with hightemperature thermal storage

A

o

185

251

203

280

Systems designed for use on a 196-

unit high rise apartment

112-113

109”113

102-141

149-177

229-232

215-223

102-141

149-177

All-electric system (shown for

reference)

Low-temperature organic Rankine

engine with seasonal thermal storage

(flat-plate or pond collectors), 100-

percent solar

o

Stirling engine system on two-axis

tracking collectors (32-percent efficient engine), fuel backup

Stirling engine system on two-axis

tracking collector (47-percent efficient engine), fuel backup

Stirling engine seasonal storage

(high-temperature storage, 47-

percent efficient engine)

“System operates 1985-2015. “ “See table 11-1.

A = Albuquerqu e O = Omah a ITC = Investment tax credit.
48 ● Solar Technology to Today’s Energy Needs

Iy. The Stirling engine systems probably are

the most speculative heat-engine cycles

shown here, but are potentially the most attractive. Their performance is roughly analogous to the high-performance photovoltaic

systems shown in the previous table.

COMMUNITY ENERGY SYSTEMS

The next cases examined involve systems

designed to meet the energy requirements of

a residential community of 30,000 persons.

The community examined is roughl y

square — about a mile on a side. The distribution of building types found in the community is summarized in table I 1-13. This

table also indicates that about 0.5 km2 o f

area is available for solar collectors on

southern-facing roofs and parking facilities.

Another 0.25 km2 would be available if all

roadways in the community could be covered with collectors. This combined area

would be nearly enough to provide all of the

Table 11-13.—Buildings in the

Community of 30,000

Typical Area

area available

available on roofs

Number on south- and parkOf ern roofs ing lots

buildings (m’) (mz

)

Single family detached

residences. . . . . . . . . .

8-unit townhouses . . . . .

36-unit low rise apartments. , . . . . . . . . . . . . .

196-unit high rise apartments. , . . . . . . . . . . . . .

Shopping center. . . . . . .

Total roof and parking

lot area. . . . . . . . . . . .

Total road surface. . . .

Total available surface

1,864 81,600 81,600

232 75,800 150,000

72 48,500 103,400

20 20,000 103,000

1 28,800 63,000

2,189 254,700 501,000

250,000

751,000

Ground area required for 100-percent solar system

in Albuquerque

Area needed (m2

)

Parabolic dishes/Stirling engines. 800,000-1,000,000

Photovoltaic concentrator system

(two-axis tracking) . . . . . . . . . . . . 1,400,000-1,800,000

Pond collectors/ORCS engine. . . . 1,900,000-2,500,000

energy needs of the community in Albuquerque if high performance engines were used.

Lower performance devices and less sunny

regions would require significantly more

area than is available from the roofs and

parking facilities, and roads and special

areas would have to be set aside for collector fields. It would be possible to greatly

decrease the energy demand in the community if a concerted energy conservation

program were implemented.

As in the previous cases, the different systems are compared on the basis of the

charges made to the energy consumers in

the community. Three “conventional” communities were selected for reference: (1) a

community with a mixture of heating and

cooling systems roughly in proportion to the

mixture actually occurring in the area being

examined; (2) a community in which all

buildings are assumed to use electric resistance heating and electric air-conditioning;

and (3) a community in which al I single family houses, townhouses, and low rise apartments use heat pumps.

The costs of providing energy to the community from a number of different solarand conventional-energy systems are compared in tables 11-14 and I i-l 5. Results are

shown assuming that the systems are owned

and operated by either a municipal utility

(which is able to finance the project from

tax-exempt bonds) or a privately owned electric utility.

Two conventional cogeneration systems

are examined:

1. A diesel-engine system burning gas and

2

using an organic Rankine system operating from the heat in the diesel exhaust to increase the performance of

the electric generation when electricity

demands are high.

A steam cycle burning coal in which

hot water is extracted for use in absorption air-conditioners and district heating.

In both cases, energy is distributed

throughout the community in two ways — as
Ch. II Overview of Onsite Solar Technology 49

Table ll-14.— Levelized Monthly Energy Costs Per Unit for a Community in Albuquerque, N. Mex.

(Municipal and Private Utility Ownership)

Energy prices increase to level shown by year 2000

(Gas prices in $/MMBtu; electricity in $/kWh)

Gas: $3.18 Gas: $4.77 –

Gas: $1.46 Elec: $0.0388 Elec: $0.0884

Percent Elec: $0.0271 Gas: $3.18 20-percent 20-percent

solar (No increase) Elec: $0.0388 solar ITC solar ITC

1977 mixture of buildings. . . . . . . . . . . . . 0

All-electric resistance heat . . . . . . . . . . . 0

Heat pumps in most buildings . . . . . . . . 0

Diesel/ORCS (gas backup). . . . . . . . . . . . 54.0

Coal steam cogeneration. . . . . . . . . . . . . 41.7

Solar steam cogeneration . . . . . . . . . . . . 70.1

Solar steam total energy with fossil

superheat (coal backup). . . . . . . . . . . . 66.4

Solar Stirling (high efficiency, gas

backup) . . . . . . . . . . . . . . . . . . . . . . . . . 91.4

Solar Stirling (low efficiency, gas

backup) . . . . . . . . . . . . . . . . . . . . . . . . . 90.4

100-percent solar, low-temperature

ORCS(60 o

-170 o,200 o F). . . . . . . . . . . . 100.0

100-percent solar, low-temperature

ORCS (90o

-180 o,200 oF) . . . . . . . . . . . . 100.0

100-percent solar, silicon concentrator. 100.0

100-percent solar heating, cooling, and

hot water, flat-plate collectors . . . . . . 67.0

100-percent solar heating, cooling, and

hot water, flat-plate collectors . . . . . . 67.0

100-percentt solar hot water and heatpond collectors. . . . . . . . . . . . . . . . . . . 54.7

100-percent solar hot water and heatpond collectors. . . . . . . . . . . . . . . . . . . 54.7

90

130

125

127 (160)

125 (165)

150 (203)

144 (193)

146 (196)

157 (207)

207 (278)

252 (338)

188 (255)

157 (213)

128 (172)

140 (175)

127 (158)

( ) = Private utlllty ownership . ITC = Investment tax credit.

electricity and as thermal energy. Hot and

cold fluids are sent to each building for

space-conditioning.

The tables also show the costs of a number of solar systems analogous to those previously discussed for use in individual buildings. Two systems not previously discussed

are

1 A system based on a heliostat field and

a central receiver which can provide

high-temperature steam to a standard

steam turbine; and

126

174

165

140 (173)

136 (175)

156 (208)

150 (199)

149 (198)

159 (210)

207 (278)

252 (338)

188 (255)

166 (222)

138 (181)

155 (191)

143 (173)

126

174

165

132 (164)

126 (164)

143 (192)

37 (184)

37 (184)

47 (195)

89 (256)

226

357

325

93 (225)

57 (195)

58 (208)

55 (202)

148 (195)

160 (207)

189 (256)

230 (311) 230 (311)

171 (235) 171 (235)

153 (205) 191 (244)

127 (168) 165 (207)

147 (181) 210 (244)

135 (165) 199 (228)

2. A system which uses solar heaters to

boil water and a coal boiler to increase

the temperature of the steam to the

“superheated” level, which results In

the most efficient steam cycle.

No easy interpretation of the results is

possible. It is apparent that most of the solar

systems do not become attractive on a

strictly economic basis unless the most

gloomy forecast of the price of conventional energy is accepted. with a tax credit

or with municipal utiIity financing, however,
50 ● Solar Technology to Today’s Energy Needs

Table 11-15.—Levelized Monthly Energy Costs Per Unit for a Community in Omaha, Nebr.

(Municipal and Private Utility Ownership)

Energy prices increase to level shown by year 2000

(Gas prices in $/MMBtu; electricity in $/kWh)

Gas: $2.39 Gas: $3.59

Gas: $1.10

Percent Elec: $0.0229 Gas: $2.39

solar (No increase) Elec: $0.0329

1977 mixture of buildings. . . . . . . . . . . . . 0

All-electric resistance heat . . . . . . . . . . . 0

Heat pumps widely used . . . . . . . . . . . . 0

Central oil heat, electric a/c, grid elec . . 34.9

Diesel/ORCS (gas backup). . . . . . . . . . . . 55.8

Coal steam cogeneration. . . . . . . . . . . . . 45.5

Solar steam cogeneration . . . . . . . . . . . . 67.7

Solar steam cogeneration (fossil

superheat) . . . . . . . . . . . . . . . . . . . . . . . 65.1

Solar Stirling (high efficiency, gas

backup) . . . . . . . . . . . . . . . . . . . . . . . . . 87.5

Solar Stirling (low efficiency, gas

backup) . . . . . . . . . . . . . . . . . . . . . . . . . 85.8

100-percent solar, low-temperature

ORCS(60°-170°,200° F). . . . . . . . . . . . 100.0

100-percent solar, low-temperature

ORCS(90°-180°,200°F). . . . . . . . . . . . 100.0

100-percent solar, siIicon concentrator

with minimum collector area. . . . . . . . 100.0

100-percent solar, siIicon concentrator

with extra collector, less battery. . . . . 100.0

100-percent solar hot water and heatpond collectors. . . . . . . . . . . . . . . . . . . 60.1

98

131

130

127 (152)

134 (170)

139 (183)

188 (253)

177 (238)

197 (264)

208 (276)

280 (371)

371 (495)

339 (460)

296 (403)

174 (221)

133

174

169

149 (174)

147 (183)

150 (194)

195 (260)

184 (245)

200 (268)

212 (280)

280 (371)

371 (495)

339 (460)

296 (403)

188 (236)

( ) = Private utlllty ownership ITC = Investment tax credit.

a number of very large solar systems are

able to compete with conventional utility

costs in Albuquerque and are surprisingly

close to the cost of the conventional cogeneration systems, As expected, the solar systems are somewhat less attractive in

Omaha, where the solar energy resource is

smalIer,

Since the thermal distribution system

adds considerably to the cost of all of the

community cogeneration systems examined,

it is possible that the community chosen for

analysis is too large for an optimum solar

community system. Much more analysis

would be required, however, to determine

Elec: $0.0329 Elec: $0.0748

20-percent 20-percent

solar ITC solar ITC

133

174

169

144 (168)

138 (173)

139 (181)

178 (240)

169 (227)

184 (248)

195 (260)

257 (343)

339 (456)

308 (423)

268 (370)

177 (222)

236

351

326

237 (261)

197 (232)

173 (215)

198 (260)

191 (248)

200 (264)

214 (278)

257 (343)

339 (456)

308 (423)

268 (370)

237 (282)

the optimum size and density of a solar

community,

INDUSTRIAL SYSTEMS

The finaI series of tables examines solar

devices used to provide energy for a large industrial plant. It is assumed that the pIant

requires a constant input of 150 MW of thermal energy and 30 MW of electric energy

throughout the year. The analysis assumes

that the factory works on three shifts, but

the solar equipment would be more attrac-
Ch. II Overview of Onsite Solar Technology ● .51

—.. — ———.——-.——.—. — . —

Table 11-16.—Assumed Conventional Energy Costs for Large Industrial Users, 1976 Dollars

1976 rates, Year 2000 rates, Year 2000 rates,

year 2000 rates, energy cost, energy cost,

projection (1) project ion (2) projection (3)

Electricity ($/kWhe . . . . . . . . . . . . . . . . . . . . A .01526 .02190 .0499

0 .01704 .02445 .0557

Natural gas—mils/kWht and ($/bbl oil

equiv.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 2.696 (4.60) 5.869 (10.02) 8.811 (15.04)

o 2.365 (4.04) 5.149 (8.79) 7.729 (13.19)

Residual Fuel Oil No. 6—mils/kWht and

($/bbl) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 6.335 (10.81) 8.856 (15.12) 20.703 (35.34)

o 5.474 (9.34) 8.025 (13.70) 17.889 (30.53)

Coal —mils/kWht and ($/ton). . . . . . . . . . . . . A 2.80 (20) 4.42 (31.55) 9.15 (65.36)

A = Albuquerque O . Omah a

—

tive if it were assumed that the factory was

not operated during the night.

In general, it is more difficult for solar

energy systems to compete with the price of

fuels conventionally used by industry. (Industrial fuel prices are summarized in table

11-16. ) Industries can use a wider variety of

fuels than residential and commercial customers, and electricity is delivered to industry at “bulk rates” which are usually considerably lower than residential and commercial electric rates The low industrial

rates are due principally to the fact that no

distribution system is required, billing services are simplified, and large industrial loads

tend to be more regular than commercial

and residential loads.

The use of solar energy in the industrial

and agricultural sectors also is hindered by

the high cost of capital used for typical investments in industrial equipment. I n many

cases, industries need to finance a large

fraction of their new plant investments with

equity and expect high rates of return on the

investments, Payback times of 1 to 3 years

frequently are expected. Widespread industrial use of cogeneration facilities based on

conventional fuels also makes it more difficult for solar energy to compete with conventional alternatives.

Three different techniques for financing

industrial equipment were examined:

1 .

2.

Financing from a conventional industry, assuming that 75 percent of the

cost was corporate equity on which a

20-percent return after taxes is expected, and 25 percent financed with

bonds;

Financing from a privately owned utility; and

3. Financing from a municipal utility (or

from low-interest bonds available from

some other source).

A variety of different direct solar devices

can be used to generate hot water for food

processing, textiles, washing, and other

industrial and agricultural applications. The

cost of operating these systems is compared

with the cost of conventional industrial

equipment in table 11-17. It can be seen that

the least expensive devices are the solar

ponds, which may cost as little as $30/ m

2

.

Energy from conventional flat-plate collectors in industrial applications costs more

than energy from roof-mounted collectors,

since field-mounted systems require foundations, mounting racks, and expensive piping

networks,
52 ● Solar Technology

to Today's Energy Needs
Ch. 11 Overview of Onsite Solar Technology ● 53

The table indicates that the pond systems

should be able to produce hot water in Albuquerque at prices competitive with oil, even

if oil prices do not increase. Solar heat in the

less-favored Omaha climate would start to

be competitive in 1985 only if oil prices are

expected to increase to $14 to $16 per barrel

by the year 2000. Virtually all of the solar

hot water systems would be competitive by

1985, if the price of oil is assumed to increase to $30 to $35 per barrel by the year

2000. Municipal utility financing, or some

other form of subsidized financing, would

make it much easier for industrial solarenergy systems to compete.

If solar hot water systems are to compete

with natural gas by 1985, it must be assumed

that industrial gas prices will rise by more

than a factor of three by the year 2000 (i. e.,

to the equivalent of $14 to $16/barrel of oil

or more). Solar units should be able to compete with the heat generated by burning hydrocarbons made synthetically from coal,

but would not be able to compete with direct combustion of coal by 1985— unless the

price of coal increased to more than $60 per

ton by the year 2000, a price increase which

seems unIikely at present.

It must be emphasized that there were

few applications where solar energy was

competitive with conventional fuels, if the

solar equipment was financed with conventional industrial-plant financing. The solar

equipment was considered “competitive” if

the Ievelized price, assuming private-utility

financing, was equivalent to the Ievelized

price of energy from conventional sources,

Low- interest “municipal” utility financing

lowers the fuel cost at which the solar

systems become competitive.

About 5 percent of U.S. energy is consumed by agricultural and industrial processes at temperatures between 5500 and

2120 F (6.5 percent, if preheat energy is

counted. ) Relatively simple one-axis tracking CoIIectors can be used to provide process heat at temperatures as high as 5500 F

(288 ‘C) Collectors for this purpose were

assumed to cost $80 to $1 40/m 2 [not including installation) and, as a result, the

solar energy provided at these temperatures

costs about twice as much as the solar energy provided by pond collectors at temperatures below 2120 F. Table I 1-17 also indicates the cost of solar energy produced at

3500 F (177 “C). It can be seen that statements made about the competitiveness of

direct solar hot water production can be applied to heat produced at this higher temperature, if it is assumed that fuel prices increase about twice as fast as assumed in the

previous statements. Since even the lowcost tracking collectors examined cost more

per pound than many types of manufactured products, it may well be possible to

reduce solar costs below those shown here.

The cost of several different solar cogeneration systems is shown in table I 1-18. Solar

cogeneration systems, using small heat

engines or photovoltaic devices, may be

competitive with conventional fossil systems in roughly the same conditions that

solar hot-water systems were shown to be

competitive. Presumably, this is because the

cogeneration systems are able to provide

relatively expensive electricity and more

useful energy per unit of collector area.

Three types of solar systems were examined:

1. A two-axis tracking system using a thin

2

3

plastic lens focusing light on a silicon

photovoltaic cell (waste heat is assumed to be collected from each cell at

1800 F and piped to a central storage

reservoir).

A two-axis tracking frame covered with

an array of mirrors focusing on a Stirling engine (waste heat at 3500 F is collected with a piping system).

A steam system using a field of mirrors

(heliostats) focusing light on a central

tower (in this case, the waste heat at

3500 F is available at the tower site).

One difficulty encountered in reviewing

the future value of solar-generated heat for

industry is that as energy prices increase, industries undoubtedly will find many places

where low-temperature heat can be recov-
Solar Technology to Today’s Energy Needs

I

I

I

I

I

I

4 0
Ch. 11 Overview of Onsite Solar Technology ● 55

—

ered from existing manufacturing processes

at relatively low cost, possibly narrowing the

market for solar equipment Conventional

cogeneration also will become increasingly

attractive as fuel costs rise. Solar cogeneration systems were able to compete with conventional cogeneration systems used in industry In sunny regions only if It was assumed that oil prices increase to more than $1 6/-

barrel by the year 2000 (the more expensive

systems required prices near $30/bbl to compete) In less-favored climates, it was necessary to assume that oil prices rose to more

than $20 to $25/barrel before solar compared favorably

It can be seen, therefore, that while a market for solar heat and electricity for industry

may develop by the mid- to late-l 980’s, the

major near-term use of solar energy in these

applications is likely to occur in situations

where conventional fuels are not readily

avaiIable or inconvenient to use, or where

increased use of these fuels is forbidden by

national standards for air and water quality,
Chapter Ill

FEDERAL POLICY FOR PROMOTING

AND REGULATING ONSITE

SOLAR ENERGY
Chapter llI- FEDERAL POLICY FOR PROMOTING AND

REGULATING ONSITE SOLAR ENERGY

Page Table No, Page

A Surveyof Policy Options . . . . . . . . . . . . . . . . . 61 2.

Policies That Would Increase the Cost

of Conventional Energy Sources. . . . . . . . 61

Policies That Would Reduce the Net Cost

of Producing and/or Purchasing Solar 3.

Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Research and Development Support. . . . . . 63 4.

Legal and Regulatory Considerations. . . . . . 63

Policies That Would Establish Foreign

Assistance Programs Involving Solar

Technology . . . . . . . . . . . . . . . . . . . . . . . . . 64

Programs in Education and Public 5<

information. . . . . . . . . . . . . . . . . . . . . . . . . . 65

Policy Options From Three Perspectives . . . . . 65

Perspective. . . . . . . . . . . . . . . . . . . . . . . . . . 65

Perpsective B.... . . . . . . . . . . . . . . . . . . . . . . 67

Perspective C, . . . . . . . . . . . . . . . . . . . . . . . . . 73

issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

Issue I. Federal Tax Laws. . . . . . . . . . . . . . . . 74

lssue 2. Financing Onsite Solar. . . . . . . . . . . 80

issue 3. Solar lnstallations on Federal

Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

lssue 4. Use of Existing Grant Programs . . . 96

The Effective Cost of Solar Energy in

Residential Buildings in Omaha, Nebr.,

[¢/kWh]WithaHigh Level of

Incentives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Property Tax Rates unselected U.S.

Cities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Authorizing Appropriations for the

Energy Research and Development

Administration, U.S. House of Representatives, 95th Congress, Conference

Report No.95-671 . .....................109

Authorizing Appropriations for the

Energy Research and Development

Administration, U.S. House of Representatives, 95th Congress, Conference

Report No.95-671 . .....................110

LIST OF FIGURES

lssue 5. Proprietary lnterests vs. Public Figure No. Page

Dissemination of lnformation . . . . . . . . . . 98 I.

Issue 6. Competition. . . . . . . . . . . . . . . . . . . . 99

Issue 7. Consumer Protection . . . . . . . . . . . .100 2.

Issue 8. Demonstration Programs . ........101

Issue 9.CoordinationofFederal R&D. ... ..103 3.

lssue l0. Priority Given to Decentralized

Soar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104 4.

lssue ll. Priorities in Solar RD&D . ........105

lssue 12. DOE Solar Funding . ............109 5.

Issue 13. SERi . ........................110

lssue 14. Staffing Limitations . ...........111 6.

7.

LIST OF TABLES

Effective Capital Costs as a Function of

Investment Tax Credit. . . . . . . . . . . . . . . . . . . 76

Effective Capital Costs as a Function

of Depreciation Schedules. . . . . . . . . . . . . . . 77

Effective Capital Costs With and

Without Property Taxes . . . . . . . . . . . . . . . . . 79

The Effect of Loan-To-Value Ratios

on Overall Capital Costs. . . . . . . . . . . . . . . . . 82

The Effect of interest Rates on

Coverall Capital Costs . . . . . . . . . . . . . . . . . . . 83

Lender Perceptions of Likely

impact of lncentive Options on

Loan Decisions . . . . . . . . . . . . . . . . . . . . . . . . 85

The Effective Cost of Capital to the

Government as a Functionof the

Discount Rate Used in Decisionmaking . . . . 92

TableNo. Page 8. The Effect of Federal Discount Rate -

l. The Effective Cost of Solar Energy in on the Perceived Cost of Federal

Omaha, Nebr., for 20 Percent investments in Three Types of Solar

lnvestment Tax Credit [¢/kWh] . . . . . . . . . . . . 72 Installations. . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Chapter Ill

Federal Policy for Promoting and

Regulating Onsite Solar Energy

One of the attractive features of onsite solar energy is that it can be developed and marketed with very little special assistance from Federal or State

governments. A small solar industry already exists and the analysis of this

paper suggests that a market for unsubsidized equipment may expand rapidly. Solar energy systems are easily compatible with existing institutions: They

can be produced by any of a large number of existing industries; financed in

conventional ways; built and operated with existing labor skills. Moreover,

they will not have a major negative environmental impact. As a result, their introduction will not need to be controlled by an elaborate set of new regulations, legislation, or regulatory agencies— modest adjustments of existing

regulations governing conventional heating and cooling equipment should

suffice i n most cases. The solar industry may not be able to have a major impact on U.S. energy supplies, however, without coherent and sustained support from Federal and State governments.

Since onsite solar technology will apparently develop without Federal incentives, it

might be tempting to conclude that the best

policy for the Government to adopt would

be no policy at all Existing Federal energy

policy, however, will affect onsite solar

energy equipment whether or not an attempt is made to develop a specific policy

for it. The energy market in which solar technology must compete is highly artificial

because of the layers of Federal regulations,

controls, and subsidies which have accumulated over the years; energy legislation

adopted during the next few years is likely

to increase the complexity of these regulations rather than eliminate them. In many

ways, current policies acting as disincentives for on site solar equipment include:

– Policies which maintain the price of

residential fuels at artificialIy low levels;

– Policies which permit tax advantages to

mining and drilling operations and larger utiIity-owned generating faciIities

but which do not provide equivalent

subsidies to onsite equipment.

– Policies which subsidize research on

centralized generating facilities without giving serious support to onsite

equipment.

The fact that these policies have the effect of reducing the cost of fossil and

nuclear energy relative to solar energy may

be largely inadvertent. They have, however,

produced a situation where a decision to

make no change in policy translates into a

decision to continue disincentives to onsite

solar energy.

Without Federal assistance, the fledgling

solar industry is likely to grow slowly. Typically, several decades are required before

major innovation moves out of a laboratory

and becomes a commercially marketable

product. In the case of solar products, there

are a number of reasons for delay, Consumer concerns about the reliability of the

technology, about the resale value of

buildings with the equipment attached, and

about the possible rapid obsolescence of

novel equipment must be allayed. Investors

and financial institutions must be convinced

that a market of sufficient size exists to

justify the investments required for mass

production. Installers, architects, code officials, and equipment designers must feel

that they have reliable and accurate i n -

formation about the costs and performance

of the equipment and about techniques for

evaluating competing designs before they

can seriously consider the options offered

by a novel technology, Insurance companies

must be convinced that risks are acceptable.

59
60 ● Solar Technology to Today’s Energy Needs

As a burgeoning technology, solar energy

faces a uniquely difficult marketing problem because it requires a large initial investment; that is, the bulk of the money spent

for solar energy goes for purchasing the

equipment rather than paying monthly fuel

bills. Thus, the attractiveness of solar equipment is generally only apparent if “life cycle

costing” techniques are used, but such

techniques are currently seldom employed

by consumers.

No matter how modest the objectives,

developing coherent and useful legislation

for onsite solar technology presents a challenging problem. Unlike the Federal programs to develop nuclear fission or fusion

reactors where a relatively small number of

organizations manufacture or purchase the

facilities, development of an adequate

policy for stimulating onsite solar equipment will require the Government to assess

the needs and preferences of large numbers

of groups and individuals, each with its own

interests. Units will be built, owned, and

operated by individuals and organizations

with skills and expectations that cover a

wide range. And, because solar technology

must be tailored for specific climates,

buildings, and energy requirements, incentives must apply to a large variety of different system concepts.

One of the greatest challenges in designing an effective Federal program in this area

will be to insure that the programs deal fairly with the diverse group of individuals and

organizations that may be affected by the

policy. It will be necessary, for example, to

find a way to deal equitably with innovations originating from organizations which

differ greatly in size. Similarly, it will be

necessary to insure that policies designed to

affect consumers provide incentives which

are accessible to persons with low incomes.

(It does little good to provide a low-interest

loan or a tax credit to an organization or individual unable to provide the downpay -

ment for a solar device. )

There will, of course, be disagreement

about the types of legislation needed in

regard to onsite solar energy generation

since different observers will have different

perceptions about the future costs, availability, and acceptability of different energy

sources; moreover, different observers will

attach different values to the environmental

and social benefits which solar energy can

offer. While there may be disagreement

about the desirability of action, however,

there is little doubt that Federal legislation

can accelerate the rate at which solar equipment enters the market, if this is judged to

be a desirable objective.

By way of caution, however, it must be remembered that the Government has almost

no history of intervening in the development

of commercial products. While it has a wellestablished role in supporting basic research

and in regulating the impact of new technologies which have become established, it has

rarely set about to nurse a specific technology out of the research laboratory and into

the marketplace. The one noteworthy example of Federal success in this area is the agricultural extension program which has, on a

continuous basis, transformed universityborn concepts into routine farming practices, Another possible example is the Federal program to develop a commercial nuclear

power program, although many in the industry seem to feel that Federal participation in

the program has been at best a mixed blessing.

Most of the products which have reached

the commercial market because of Federal

development funding have been serendipitous “spinoffs” from projects sponsored by

the -Department of Defense or by the National Aeronautics and Space Administration. In these cases, the commercialization

process was not a goal of the Federal support program, but rather resulted because

the Federal contract enabled the company

to develop equipment and expertise needed

to meet a commercial application. Some

outstanding examples are the transistor industry developed by Texas Instruments and

other companies as a result of space and

defense requirements and the Boeing 707 jet

aircraft which grew out of that company’s

design of the military KC-1 35.

,>
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 6 1

It is important to recognize that there are

dangers associated with overzealous Federal participation in the development of commercial products. A poorly designed program can interfere with the normal development of business relationships, promote inferior products, encourage the wrong enterprises to enter the field, and otherwise

distort the development of normal markets.

It is certainly possible to find examples

where Federal efforts to alter existing

market structures have failed. The “operation breakthrough” program, an attempt t o

reshape the home building industry in the

image of the aerospace companies, wouId

almost certainly have been designed very

differently if the Government had had an

adequate grasp of the real problems faced

by builders.

Successfully administering a program for

the commercialization of solar technology,

with its complex matrix of problems and opportunities, will severely tax Federal bureaucracies accustomed to dealing with

small numbers of well-structured projects.

An effective program will require imagination, flexibility, and a willingness to try new

ideas and live with some mistakes.

A SURVEY OF POLICY OPTIONS

Before turning to a more detailed discussion of the different kinds of incentives

available, it may be useful to review the

kinds of policy options which have been proposed for promoting and regulating solar

energy, and the Iikely effects of each:

POLICIES THAT WOULD INCREASE

THE COST OF CONVENTIONAL

ENERGY SOURCES

One of the simplest and most powerful

ways to provide incentives to solar equipment wouId be to increase the cost of conventional fuels. This could be done by (a)

removing implicit subsidies, (b) freeing

prices from controls, or (c) taxing the energy

sources directly. This technique would require virtually no net Federal expenses and

would require the least Federal involvement

in decisions made by the free market. Increasing the cost of conventional energy

sources could be justified solely on the basis

of the need to conserve those resources

which are being rapidly depleted under the

current price structure. It could also be

justified as an attempt to have prices include such external costs as environmental

damage, social disruption, the indirect drain

on foreign-exchange resulting from oil imports, and national security risks.

A policy of increasing the cost of conventional energy would clearly not be without

problems. Such a policy would create inflationary pressures and the burden would be

borne most heavily by people with low incomes unless some compensating mechanism of repayments can be found. Continuing our present course of increasing oil imports, with the attendant balance of payments deficits problems which such policies

create, can also be inflationary. It is unclear

how long Federal policy

maintain U.S. fuel prices

levels while world prices

There is reason to believe

preferable to encourage a

will be able to

at their current

increase rapidly.

that it would be

gradual increase

rather than to find prices growing explosively during a short interval.

POLICIES THAT WOULD REDUCE THE

NET COST OF PRODUCING AND/OR

PURCHASING SOLAR EQUIPMENT

Policies designed to accomplish this objective fall into four basic categories:

1. Providing financial incentives to poten-
62 ● Solar Technology to Today’s Energy Needs

tial owners to encourage them to purchase solar equipment, thereby

creating an expanded market and justifying mass production. Techniques for

accomplishing this include:

–Giving income tax credits and allowing accelerated depreciation techniques (see Issue 1). *

– Removing barriers to obtaining

financing for solar equipment (see

Issue 2).

–Encouraging States and municipalities to exempt solar equipment from

property taxes and sales taxes (perhaps by providing Federal payments

to States in compensation for lost

revenues, see Issue 1).

— Permitting tax exemptions for income derived from loans for solar

equipment.

— Enhancing consumer confidence in

equipment by developing a system of

unified performance standards by

certifying (and perhaps subsidizing)

testing laboratories (see Issue 7), and

by ensuring proper training for building inspectors.

These incentives could have a significant

effect on the perceived cost of solar equipment. One potential problem, however, is

that although tax incentives would minimize

Government interference in the free market,

they could so reduce the risks of purchasing

novel equipment that an opportunity would

be opened for fraud through the marketing

of unreliable systems. This prospect could

be diminished by requiring that all who wish

to qualify for incentives must purchase only

equipment that meets minimum Federal

standards. A balance must be found between the desire for a free market and a

need for Government oversight.

2. Using Federal purchases of solar devices to stimulate the market by adver-

*These numbers refer to the next section of the

report, which is organized around several crucial

issues and provides a more complete discussion of

these topics

3.

tising and demonstrating their utility

(see Issue 3).

Providing direct incentives to manufacturers of solar equipment in one or

more of the following ways:

— Loan guarantees and loan subsidies.

–Tax relief similar to that discussed

for equipment purchases (i.e., investment tax credits, or accelerated depreciation allowances).

–Cost-sharing through direct grants

(see Issue 4).

— Encouragement of exports (particuIarly to developing countries).

Incentives to manufacturers could be extremely useful today, since solar equipment

is developing rapidly. Manufacturers are

understandably reluctant to invest in production equipment that they feel may soon

become obsolete. This reluctance could be

reduced considerably if they were permitted

to “write-of f” manufacturing equipment

over a relatively short period through accelerated depreciation allowances. Another

problem for firms attempting to market a

new concept, availability of financing, can

be particularly troublesome for small companies lacking established relationships with

lending institutions.

Designing an effective policy for assisting

manufacturers of solar equipment will require overcoming a difficult problem. It is

desirable to ensure that the results of federally sponsored development programs are

widely disseminated and utilized. If the

company performing the research is unable

to maintain any proprietary interest in the

product developed, however, it may be reluctant to invest in production (see Issue 5).

It will be necessary to ensure that no organization gains monopoly control over crucial areas of the solar industry and to ensure

that small businesses are fairly treated (see

Issue 6).

4. Providing assistance in developing

equipment standards and a testing capability in private testing la boratories..
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 63

This assistance would be valuabl e

because it could help to alleviate concerns

about performance and reliability which

have been a major barrier to sales.

RESEARCH AND DEVELOPMENT

SUPPORT

Federal support for basic research and development of small solar energy equipment

can clearly accelerate the rate at which new

types of solar devices reach the market. The

investment required to develop most of the

onsite equipment considered in this assessment may be consistently smaller than that

needed to develop operational systems using synthetic fuels, fusion, or advanced fission reactors. As a result, it should be possible to explore a wider range of small, onsite

technologies than if the same amount of

funds were invested in developing technology for larger, more centralized equipment.

This means that investments can be made in

promising, but high-risk projects without

committing large amounts of Federal capital.

On the other hand, if the Federal Government does not provide the relatively modest

funding required for development of onsite

solar equipment, the effect will amount to a

disincentive; that is, the current disproportionate Federal research emphasis on nonsolar technologies would place solar equipment at a disadvantage in relation

sidized energy supplies

LEGAL AND REGULATORY

CONSIDERATIONS

Policies Governing the Relationship

Between Utilities and Onsite

Generating Equipment

to subThe vast majority of all energy consumed

in the United States is generated and sold by

electric and gas utilities utilizing large, centralized equipment. As a result, State laws

and regulations governing the operation of

smalI energy generating equipment are frequently archaic, and sometimes confusing,

In some cases, they can present serious barriers to the use of onsite equipment:

– In some States the owner of an apartment building or shopping center would

apparently be unable to sell solar-derived energy to clients or customers

without filing as a public utility. The

procedural complexity of operating as

a utility wouId almost certainly prevent

the installation of onsite equipment.

— Laws establishing the right of utilities to

own and operate energy generating

equipment located in buildings not

owned by utilities are frequently unc I ear.

—There is no well-established procedure

for ensuring that utilities will provide

backup power for onsite equipment at

rates which would be fair to all parties,

and there are no procedures governing

the rates at which utilities should purchase energy from onsite generating

systems during periods when such facilities are generating more energy than is

needed onsite. The analysis of the legal

aspects of onsite energy equipment

which appears in chapter VI of this report indicates that these utility-related

problems are the principal legal and

reguIatory issues Iikely to require immediate attention.

Policy alternatives for dealing with these

issues fall into two categories:

1. Policies designed to clarify the rights of

owners of onsite energy equipment Alternatives include:

— Exemption of onsite equipment from

regulation by public utility law (some

definition will be required to distlnguish “onsite” equipment from conventional utility equipment),

— Establishment of the right of owners

of onsite energy equipment to purchase power from existing utilities at

fair rates.
64 ● Solar Technology to Today’s Energy Needs

— Establishment of the right of owners

of onsite energy equipment to sell

energy to electric utilities at fair rates

2. Policies designed to encourage utility

ownership of onsite equipment, to perm it flexibility in joint ownership projects, and to clarify the difficulties

which might arise if a utility owned or

operated equipment located in buildings not owned by the utility.

The techniques available for implementing these utility policies depend critically on

whether a statement of Federal jurisdiction

in this area, such as the one contained in the

proposed National Energy Act of 1977, becomes law. If Congress finds that “the

generation, transmission, and sale of electric energy and the transportation and sale

of natural gas affect interstate commerce,

and that adequate and reliable supplies of

electric energy and natural gas are necessary for the general welfare and national

security,” 1

the options discussed above can

be directly implemented by Federal legislation requiring State utility commissions to

impose the reguIations and procedures recommended. Otherwise, the Federal Government’s power would be Iimited to persuasion, encouragement, and perhaps the provision of analytical support and guidelines for

the recommended policies.

Sunrights

Another area which requires some attention is the issue of “sunlights. ” Although

there are presently no Federal laws designed

to protect the right of an owner of solar

equipment to have adequate access to sunlight, the analysis prepared for this study has

indicated that probably none will be needed. The Federal Government could, however, facilitate efforts along these Iines being made by State and local regulatory

bodies. Options include the following:

— States could be encouraged to require

new subdivisions, commercial malls,

‘ Proposed National ~ nergy Act of 1977, SectIon 501

(a)

and industrial parks to formulate covenants which will protect the sunrights

of al I property owners,

–The Federal Government could subsidize training programs for local planners and zoning officials which would

help them to use local regulations more

effectively to protect sun rights.

— The Federal Government could encourage States to confirm the rights of individual property owners to negotiate

easements guaranteeing Iight and air,

as has already been done in Colorado,

and help prepare standard forms and

recording procedures,

—A requirement to assess solar energy

impacts could be added to the Iist of

factors which must be considered in

evaluating federally sponsored or regulated building projects, State governments could be encouraged to follow

suit.

POLICIES THAT WOULD ESTABLISH

FOREIGN ASSISTANCE PROGRAMS

INVOLVING SOLAR TECHNOLOGY

These foreign assistance programs would

have the objective of relieving stress on

world fuel markets by helping to provide the

means to use locally available energy. Such

programs could also stimulate an overseas

market for onsite solar equipment developed and possibly manufactured in the

United States. Options for Federal policy include:

– Ensuring that onsite solar energy technologies be included in programs for

foreign economic assistance whenever

appropriate,

—Subsidizing the training of foreign nations in the skills needed to design,

manufacture, and instalI solar equipment.

—Augmenting the funds available to international lending institutions for

loans related to solar energy equipment.
Ch. Ill Federal Policy for Promoting and Regulating Technology ● 6 5

–Providing a continuing international

flow of information about products,

technical developments, analytical

work, and other progress made in solar

equipment.

—Tailoring the U.S. research program to

maximize its usefulness internationally

whenever this is possible. (For example,

if a choice between a complex and a

simple approach is difficult. The decision may be tilted in the direction of

developing a simple system, if international needs are considered. )

PROGRAMS IN EDUCATION AND

PUBLIC IN FORMATION

One of the barriers to the introduction of

onsite equipment is the shortage

tects, builders, system designers,

and operators familiar with the

problems and advantages of the

This could be remedied in a variety

of archiinstalIers,

practical

equipment.

of ways:

–A program offering federally funded

fellowships and scholarships in engineering and architectural programs.

POLICY OPTIONS FROM

Selection of a specific set of policies from

the catalog of options just discussed is not

an easy process since such decisions must

be made without the comfort of confident

forecasts about the long-term costs of solar

or any other energy technology. Moreover,

political judgments must be made about the

ultimate value of the potential benefits of

solar equipment which cannot be evaluated

in conventional economic terms. The following section discusses three different perspectives on these issues, and presents

groups of specific policies which might be

chosen to meet each objective.

PERSPECTIVE A

It is sometimes argued that the Nation’s

energy requirements can be met, at least for

— Federal assistance for midcareer training in the problems of designing energyefficient buildings and industrial systems for architects, engineering consultants, and other relevant groups.

This could be done under the auspices

of existing trade associations.

—A program subsidizing labor union

training programs designed to develop

additional skills needed to install and

operate on site energy equipment.

Another problem is the fact that most

potential customers for onsite equipment

wilI not consider it as a serious alternative

when making purchasing decisions simply

because they are unfamiliar with the approach. This could be remedied to some extent with programs designed to bring life cycle costing to the attention of prospective

buyers (possibly through the auspices of

lending institutions). It might also be useful

to conduct brief training programs for professionals in a position to affect the decisions made by their organizations about

building designs and the purchase of energyrelated equipment,

THREE PERSPECTIVES

the next several decades, by gas, coal, and

nuclear sources — and without dramatic cost

increases, a dangerously high proportion of

imports, or unacceptable environmental

risks. Adherents of this position believe that

these sources will last until their use is

superseded by a new technology — fusion

being the most commonly mentioned. It is

assumed that this new technology will provide energy at prices very close (in constant

dollars) to those charged for electricity today. In this view, solar energy would play

only a minimal role; indeed, its only function would be to serve as a kind of insurance

against the failure of fusion to develop into

a usable technology.

From this perspective, it is logical that

Federal policies concerning solar energy
66 ● Solar Technology to Today’s Energy Needs

should be limited to: (a) those designed to

eliminate obstacles to development and use

of the technology, and (b) those providing

for basic research. Such research would be

of a comparatively low priority and could

not be expected to have an impact on the

commercial energy market for many years.

The resources committed to the effort

would be relatively modest.

In more specific terms, the following

policies would appear to be consistent with

Perspective A.

POLICY OPTIONS FOR PERSPECTIVE A

Incentives for Owners of Buildings

1 .

2

3

4

5.

Amend the National Housing Act to

make it clear that Federal Housing Administration (F HA) insurance can be

given to solar energy projects under

Title I (for retrofit of solar devices and

for mobile homes) and under 203b (for

new construction).

Amend the Federal Home Loan Mortgage Corporation Act (FHLMCA) so that

the Federal National Mortgage Association will be empowered to provide a

secondary market for mortgages and

loans covering onsite solar energy

equipment.

Amend the National Housing Act to

permit Federal Housing Administration

Title I funds to be used as second mortgages associated with Farmers Home

Administration (FmHA) loan guarantees.

Provide funds to ensure that techniques

for measuring the performance of collector and storage systems are developed by the National Bureau of Standards or its designers and that these techniques are rapidly communicated to

private testing laboratories.

Require that all collectors and onsite

storage systems sold be accompanied

by literature clearly showing the equipment’s standardized performance characteristics as measured by reputable

laboratories.

Programs to Provide Information About Solar

Equipment and Education Programs for

Designers and Installers

1 .

2

3.

4.

5

6

Require that any energy audits conducted of Federal buildings, and any

standards established for Federal purchase and rental, include an analysis of

the potential contribution of solar energy equipment for heating, cooling, and

cogeneration.

Require similar energy audits of all

housing and building projects which receive any Federal assistance or which

are under the jurisdiction of Federal

agencies (this would include public

housing, housing repossessed under defaults in FHA, Veterans Administration

(VA), and FmHA loan guarantee and insurance program s,)

Provide midcareer training for public

officials in a position to make judgments about buiIding designs and energy-related equipment for Federal buildings. Such training wouId famiIiarize

them with solar technologies, design

alternatives, and techniques for evaluating their economic merit.

Subsidize midcareer training programs

for architects, engineers, and interested

builders.

Establish a university fellowhsip and

scholarship program which would provide training in areas of science and

engineering relevant to solar energy

development programs.

Develop standards for emerging solar

equipment and certify testing laboratories.

Research and Development

From this perspective, the most profitable

strategy would be to fund a number of basic

research projects, looking for ways to dramaticalIy reduce costs or improve the performance of solar equipment. An orderly

procedure would be developed to test the

many advanced concepts which have been
Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy ● 6 7

proposed before making any decision about

large-scale demonstrations.

Analysis of Policy Options Above

1.

2.

A

and

Effectiveness. – These policy opt ions

have limited objectives. They would

remove obvious impediments to wider

use of solar technology, but they would

not greatly accelerate the rate at which

solar equipment enters the market.

Commercial markets could well overtake federalIy sponsored efforts.

Cost.– Since most of the elements of

this policy are regulatory in nature, the

proposals would cost very little. The

only direct expense involved would be

for energy analyses of buildings (investments which should be cost-effective)

and training programs.

PERSPECTIVE B

second view holds that the future price

availability of all nonsolar fuel sources

is very uncertain and that solar-based technology holds real promise of playing a major

role in supplying energy in the near future.

Those who accept this view also believe that

the real price of fossil fuels could increase

by as much as as a factor of 2 or 3 and electricity prices increase by as much as 50 percent over the next two to three decades and

that the price levels for energy produced by

such planned nonsolar technologies as fusion may be high enough to make solar technology competitive.

Thus, they feel that solar technology

should be treated on an equal basis with all

other promising new energy sources. This

perspective would require additional Federal action as outlined below.

POLICY OPTIONS FOR

PERSPECTIVE B

All of the Policies Discussed Under

Perspective A (except as modified below)

Incentives to Stimulate Market

1.

2.

All owners would be given an investment tax credit of 20 percent on qualifying solar equipment (including heating, cooling, process heat, heat pumps

and other applications requiring mechanical drives, and electric generation). After a 5-year experiment with

these incentives, depreciation schedules would revert to standard and tax

credits would be reduced to 10 percent.

Homeowners and owners of residential

apartment buildings, however, would

retain the right to use credits and

depreciation schedules permitted for

industry. Refunds would be made if the

credits exceeded tax Iiability.

An easy-to-use computer program

would be subsidized to evaluate the effectiveness of a variety of solar hot

water, space-heating, cooling, and electric generating systems which may be

used on typical building types. The program would be adjusted for each climatic region and would need to be updated annually to maintain current information about costs and performance. Such a program could be developed by the American Society of Heating, Refrigerating, and Air-Conditioning

Engineers (ASH RAE) or some other professional society with Department of

Energy (DOE) support. It should be flexible enough to reflect local climatic

conditions and building costs, and to

assess the potential of the equipment

when used on a number of typical

building types. It should provide practical information about anticipated initial and life-cycle costs, which should

be based on a predetermined consumer

discount rate (perhaps 10 percent for

homeowner-owned units and higher for

commercial systems). Life-cycle costing

would be based on an assumed rate of

increase in conventional energy costs

to be established by DOE. The program

should be accessible on a time-sharing

basis via computer terminal and telephone from as many regions as possi-
68 ● Solar Technology to Today’s Energy Needs

3.

4.

5.

ble. It should be made simple to understand, easy to operate, and inexpensive

to run.

The National Housing Act, the Serviceman’s Readjustment Act, and the acts

establishing the Federal National Mortgage Association (FNMA), the Federal

Home Loan Bank Board, and the Farmers Home Administration could be

amended to require that all applications for guarantee, or mortgage insurance, and all mortgages eligible for

repurchase by FNMA or the FHLMA be

accompanied by a document showing

that the building has been reviewed for

energy efficiency under an approved

procedure which includes assessment

of the potential of solar equipment.

The Federal analysis program described

above could be used for this purpose.

This would permit both the prospective

borrower and lender to review the current and future costs of supplying energy for the building and to give both parties an opportunity to analyze the value

of solar equipment in reducing these

costs. It would, in effect, be equivalent

to legislation requiring that the efficiency of consumer products be clearly

shown whenever the items are sold.

All Federal buildings, including defense

installations in the United States and

abroad, and all buildings operated under Federal auspices (e.g., public housing, repossessed housing) wouId be reviewed to establish the cost effectiveness of solar equipment. Funds

would be provided for retrofit installations wherever cost-effectiveness was

established. The Administration should

be instructed to determine the circumstances under which existing appropriations to subsidize operating costs of

federally owned buildings and buildings operated with Federal subsidies

could be diverted to capitalize solar

equipment under current legislation

and regulations.

The Adminstration should be required

to examine the following grant programs to determine what funds appropriated in these areas can be used to

subsidize the purchase of solar equipment (see Issue 4 for details):

–The community development block

grants.

– Housing rehabiIitation programs

(Section 21 3).

– Homeowner grants (Section 302).

— Homeowners incentive demonstration programs (Title IV).

— Housing finance interest subsidies.

– Funds allocated by the Energy Conservation and Production Act for renewable technologies.

–Grants administered for energy conservation by the Administration on

Aging (HE W).

—Grants administered for energy conservation by the Social Services Administration.

— FmHA grants for improving rural

homes so that they can meet code requirements.

– Grants made under the Public Works

and Economic Development Act.

–Any other grant programs which the

Administration feels might be used to

purchase solar equipment.

Incentives for Manufacturers

1. Allow qualifying manufacturers of so2

Iar equipment a 20-percent tax credit

and 3-year depreciation allowances on

machinery used in producing solar

energy equipment. These incentives

would apply to equipment purchased

during the next 5 years.

Require the administration to conduct

a study that would evaluate the desirabiIity of a variety of alternative costsharing programs which would be effective in subsidizing manufacturers’ relevant research in solar energy, which

could be made available to the public
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 6 9

in some form, and yet at the same time

protect the patentabiIity of devices developed in part with private funds.

3. Measure cost sharing in terms of the

4

fraction of a company’s total assets

which it is willing to make available for

Federal cost sharing (instead of requiring smalI companies to compete directly with larger concerns in total dollars

available for cost sharing).

Subsidize the development of a computer model which would facilitate the

analysis of the detailed performance of

a variety of different onsite solar

devices attached to realistic building

and industrial loads. Ensure that the

widest possible group of system designers and engineers have access to the

program, (An attempt should be made

to ensure that existing work in this area

is not duplicated. The Canadian Government, for example, has apparently

developed a similar program for use by

Canadian designers).

Research, Development, and

Demonstration (RD&D)

A balanced program of research, development, and demonstration should be developed and carefulIy integrated with the requirements of the industries which will

manufacture, install, and support the equipment developed. The program should incIude the folIowing areas:

PASSIVE HEATING AND COOLING

Work needs to be done to design and

make instrumented tests of buildings

matched to a large variety of climatic conditions Other research topics in this area

which would benefit from additional work

include:

●

●

●

Computer simulations of passive building designs.

Studies of retrofit potential of passive

buildings,

Demonstration of passive facilities for

livestock, storage, and other nonresidential application

ACTIVE SPACE-HEATING SYSTEMS

AND SOLAR WATER HEATING

A number of advanced collector designs

(used both for heating and air-conditioning)

remain in preliminary stages of development. Devices include improved plastics for

inexpensive colIectors, air-inflated collectors, nontracking concentrators, tubular collectors with and without simple concentrators, simple booster devices, one-axis

tracking devices using mirrors or lenses, and

a variety of other systems.

SOLAR COOLING

Solar cooling is not a commercial technology but a number of different concepts are

ready, or nearly ready for demonstration.

These include advanced absorption, adsorption, and Rankine cycle devices and integrated total energy systems with fossil fuel

used as a backup.

AGRICULTURAL AND INDUSTRIAL

PROCESS HEATING

A number of commercial products are

available in the lower and intermediate temperature ranges.

Demonstrations in

clude:

— Drying for agricultural

this area shouId inproducts ;

— Desalinization;

– Process water for washing, textiles, paper, food processing, and other IO Wtemperature applications; and

— Irrigation pumping,

Research work would include the development of inexpensive collectors for low

(150° to 250° F) temperature, intermediate

temperature (250° to 500°F) and high temperature (greater than 5000 F) applications.

THERMAL STORAGE

A variety of techniques have the theoretical potential for providing large amounts

of thermal storage at very low cost. Development of such technologies would remove
70 ● Solar Technology to Today’s Energy Needs

many of the problems faced in providing

backup power for solar energy devices. It

should be possible, for example, to build

systems capable of providing 100 percent of

the heating and hot water requirements of

apartment buildings or clusters of houses using large tanks of water (with earth providing the principal insulation), ponds,

trenches full of hot rock, aquifer storage of

hot water, storage in in-situ rock, and other

techniques. Research in more advanced

thermal storage systems (multiple tank, salt

gradient, phase change, organic and inorganic chemical reaction devices, etc. ) is

also needed and much work remains incomplete.

SOLAR THERMAL ELECTRIC

work needs to be done on development

of collectors, integration of solar devices

with end-use equipment, improved heattransfer systems, receivers, heat engines,

and many other components which would

increase design flexibiIity and reduce costs.

Development of low-temperature Rankine engines, high-temperature Stirling and

Brayton cycle engines, and improved small

steam cycle systems is needed. Research in

advanced materials (particularly ceramics)

would be useful for both colIector and engine designs.

Work on systems integration needs to be

done to identify promising concepts in a

broad range of potential applications of

smalI and intermediate size.

Research on electric storage systems is a

critical factor. Work is needed on a number

of advanced Iead-acid, high-temperature,

aqueous, and REDOX batteries, as welI as in

mechanical storage concepts such as flywheels, underground pumped hydro, and

others. Thermochemical storage systems

could greatly reduce the cost of storing and

transporting solar energy for use in thermoelectric systems and in direct high-temperature process applications.

PHOTOVOLTAICS

Areas where research would be useful incIude:

–Advanced research on amorphous

silicon, thin film materials (e. g., CdS, IIIIV heterojunctions, organic substances

and dyes), amorphous silicon, polycrystalline silicon, concentrator cells

(GAA1As, multifunction cells, high efficiency silicon thermophotovoltaic devices, interdigitated back contact cells,

vertical multifunction cells, etc.). Basic

research on semiconductor properties

of interesting materials.

–Systems analysis and engineering of

control systems for practical application, installation problems, mounting

racks, cleaning, cogeneration studies

and designs, heat exchange designs,

plumbing, etc.

–Silicon solar array technology (pilot

plant for polysilicon production, fullscale demonstration of advanced crystal growing and slicing machinery, subs idizing design of large-scale fabrication

and production facilities, advanced encapsulation, etc),

—Concentrator development (unique

problems associated with cell attachment, cogeneration, heat rejection) for

a range of concentrators including: dye

concentrators, lens, and mirror systems.

DISSEMINATION OF RESULTS

Ensure that results of Federal RD&D programs exploring technology for heat engines, thermal and electric storage, collector

designs, and other subsystems which can be

used in onsite solar energy equipment are

widely disseminated to the diverse community of institutions and individuals working on onsite solar equipment.

DEMONSTRATION AND RESEARCH STRATEGY

Develop and propose a program for the

demonstration of a comprehensive spectrum of onsite solar energy systems. This

would include (but not be limited to) the

following:

— A detailed plan for the demonstration

of the range of solar thermaI and solar
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 7 1

electric facilities from existing simple

hot-water and heating systems to larger,

more complex, and perhaps more experimental devices

—A systematic program for developing

and demonstrating a large number of

subsystem technologies which are applicable to small onsite units but which

could be enlarged or aggregated for

larger systems. For example, concentrating collectors developed for onsite

applications could provide valuable information on designs that would be useful in larger facilities Smaller demonstrations would permit a greater variety

of technologies to be tried.

– A strategy for identifying intermediate

and long-term markets for onsite solar

energy systems. The plan shouId examine a variety of potentiaI applications,

the significance of regional variations

in climate, energy prices, and other factors.

A fixed sum should be set aside with the

single purpose of funding innovative smallscale energy technologies that show promise These monies would be distributed as

direct prizes or grants to all types of inventors in typical amounts of $50,000 to

$100,000 The selection of these projects

should be performed by panels of qualified

experts drawn from a broad cross-section of

equipment developers and designers, incIuding, among others, Independent inventors, manufacturing firm researchers, university engineering and science staffs, consuIting engineers, and personnel from Government laboratories Application procedures should be as simple as possible to

encourage broad participation; the program

should be widely advertised; and winners

shouId be announced with fanfare,

Develop a system to subsidize proposals

made by smaII organization. This might incIude a procedure by which brief submlssions from quaIifylng small businesses

wouId be screened for InitiaI technical merit. SmaII grants might then be awarded to

assist them in developing the proposaI.

Underwrite the testing of solar equipment

developed by small companies, such testing

to be conducted in Federal or private laboratories.

Foreign Assistance

1.

2

3

4

5

6

Ensure that programs developing priorities for Government-supported research and federally sponsored studies

include an assessment of the potential

for overseas sales.

Encourage the development of skills

related to solar energy in developing

nations by providing fellowships as a

part of an economic assistance program,

Encourage and expand joint research

ventures with other governments and

international organizations engaged in

solar energy research.

Augment U.S. contributions to international lending institutions with the objective of encouraging onsite solar

energy facilities in developing nations.

Provide foreign aid in the form of technical assistance for demonstrating onsite solar systems in less-developed

countries

Any proposal for foreign economic

assistance involving energy must consider onsite solar equipment on an equitable basis. Training should be provided

for United Nations, Agency for lnternation Development, and Peace Corps officials planning such programs. Outside

experts in this area should be utilized to

facilitate a review of proposals.

Policies Affecting Public Utilities

Assuming that involvement in regulation

of public utiIities by the Federal Government has been established as a legitlmate

activity under the “interstate commerce

cIause‘‘ of the Constitution, the folIowing

policies could be established by Federal

Iegislation.

1. No organization which generates less
72 ● Solar Technology to Today’s Energy Needs

than 5 MW of thermal or electric energy will be regulated as a public utility

unless this status is desired by the

organ i z at ion, In the latter instance,

conventional reguIatory procedures

wouId apply. The nonregulated organization wouId be permitted to generate

and sell energy to all consumers in its

immediate area, without Iimitations on’

the prices charged or income earned. A

study should be commissioned to determine if this size threshold should be increased.

2. No organization which generates less

than 5 MW of thermal or electric energy shall be required to obtain a certificate of convenience and necessity

from local utility regulatory commissions in order to construct a plant

(unless it has asked to be regulated

under existing utiIity statutes).

3. The Administration should be instructed to examine the Sherman and

Clayton Antitrust Acts and the Public

Utility Holding Company Act to determine whether they prevent utilities

from owning onsite energy equipment.

If they do so, amendments should be

proposed which would remove such

barriers.

4. Any studies conducted by utilities to

determine fair pricing policies for selling electricity and for purchasing electricity from industrial “cogenerators”

must be expanded to include an analysis of the costs of supplying backup

power to a variety of types of onsite

solar electric generating faciIities.

Effectiveness

It is always somewhat perilous to forecast

the impact of any program for providing tax

subsidies since consumer behavior can be

unpredictable. Table I I l-l indicates the effect of a 20-percent tax credit on the perceived cost of solar energy provided by a

variety of different types of solar equipment, assuming that consumers utilize a life

cycIe costing technique to determine average energy costs. It can be seen that the tax

credit would have the effect of reducing the

cost of solar energy by 0.5¢ to 3¢/kWh. The

more the solar system costs, the greater the

tax credit and the greater the effective Federal subsidy. The table also shows the cost

of the subsidies to the Government as a resuIt of loss of tax revenues. The direct costs

shown, however, significantly overestimate

the net cost of the subsidies because extra

tax revenues will result from production inTable 111-1 .—The Effective Cost of Solar Energy in Omaha, Nebr.,

for 20 Percent Investment Tax Credit [¢/kWh]

—

—

20 percent Direct

No Investment Federal

Incentive s Tax credit subsidy ●

—

Solar hot water . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,0- 4.2 1.4-3.3 0.6-0.9

Solar heating and hot water. . . . . . . . . . . . . . . . . . 3.0- 7.7 2.0-6.6 1.0- 1.1

Heating and hot water with seasonal storage . 3.8- 6.9 2.5-4.7 1.3-2.2

Solar heating hot water and cooling . . . . . . . . . . . . . . 6.0 4.0 2.0

Solar Photovoltaic electricity. . . . . . . . . . . . . . . . . . . . 3.8-11.8 2.8-9.1 1.0-2.7

—..

‘This IS the effective cost of the subsidy to the Government rellting from the tax revenues because of the tax credits It IS

calculated assuming that the Government applles a 10 Percent discount rate to future costs (See text )

Assumptions 1985 startup of equipment

The price ranges reflect the cost differences expected in the variety of resldential equipment see Volume II

Chapter IV
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy Ž 73

creases by businesses manufacturing and installing solar equipment, and from increased

sales in supporting industries, such as the

manufacture of glass and primary metals.

This revenue would at least partially offset

the direct revenues lost because of the

credits I t a dolIar is spent on solar equipment manufactured in the United States

rather than on imported oil, the U.S. gross

national product (GNP) could be increased

by $2 to $5 Since the average Federal tax

revenue per dolIar of GNP is about 20 percent, an incentive which encouraged a dollar Investment in solar equipment could

yield as much as $().40 to $1.00 in added Federal tax revenue Since this revenue would

be obtained close to the time when the subsidy was granted, its “present value” to the

Government would be high.

Reducing the price of solar equipment

also would be expected to expand sales and

thereby encourage the introduction of mass

product ion equipment in technologies

where such equipment can be used effectively.

PERSPECTIVE C

A third perspective is an extension of the

view just discussed (Perspective B). It contends that the cost of energy could soon

climb rapidly because of increasing competition for limited supplies. In this view, the

virtues of solar energy — notably its benign

impact on the environment, its desirable impact on labor, its impact on reducing competition on world energy supplies, its ability

to avoid monopoly ownership of energy

sources, and its potential for reducing the

risks of climatic change and nuclear proliferatlon — merit an aggressive promotional

program, even if the technology is not expected to become fulIy competitive in conventional economic terms.

POLICY OPTIONS FOR

PERSPECTIVE C

An example of the policies which would

be added under this perspective include:

1.

2.

3,

4.

5.

6.

7.

All of the policies discussed under

Perspective A and B except as strengthened below.

All owners would be given an investment tax credit of 20 percent on qualifying solar equipment (including heating, cooling, process heat, mechanical

drive, and electric generating devices)

and would be permitted to depreciate

solar equipment over a 5-year interval,

These incentives would continue until

Congress determined that they were no

longer required to ensure the competitiveness of solar equipment.

The income from all loans made for

solar equipment would be exempt from

Federal taxation.

All manufacturers of solar equipment

would be given an investment tax credit

of 20 percent on qualifying manufacturing equipment over a period of 5

years. These incentives would continue

until Congress determined that they

were no longer required to ensure the

competitiveness of solar equipment.

Federal purchases of onsite solar energy equipment would be required for existing and new Federal buiIdings constructed with Federal support, in all

cases when it could be shown that the

technology would be cost-effective

based on a low discount rate (e. g., 3 percent) and a high assumed increase in

the cost of conventional energy,

FHA minimum property standards

would be required to include onsite

solar equipment whenever an analysis

demonstrated that the equipment

would be cost-effective on the basis of

approved analytical techniques discussed previously. (As a possibl e

variant of this approach there might be

a provision for subsidized interest rates

to cover the incremental cost of solar

equipment. )

Utilities would be required to inform all

residential and small industrial and

commercial customers of the savings
74 . Solar Technology to Today’s Energy NeedS

8.

9

10,

11.

they might realize by instalIing a variety of different types of onsite solar

equipment. The utilities also would be

required to provide installers and financing for any projects selected by the

owners of the buildings. The utility

would be reimbursed with charges added to the owner’s bilI over a 10-year

period. (This is similar to the program

for insulating buildings proposed in the

National Energy Plan. )

The price of electricity would be raised

to a rate which reflects the marginal

cost of providing electricity from the

most recent plant placed online. And

the price of oil would be raised to

refIect the cost of adding additional oil

supplies. The funds generated by the

taxes required to do this would be redistributed in the manner proposed by the

National Energy Plan.

It would be determined that the development of low-cost solar coIIection,

conversion, and storage equipment is a

major national priority. An aggressive

research and marketing program with

ambitious goals for cost reductions and

installed capacity would be funded at a

rate which would reflect the urgency of

the priority given

A separate section of the Small Business Administration would be established solely to guarantee loans made

for manufacturing equipment used to

produce solar equipment.

Environmental legislation would be

strictly enforced, conventional powerplants held to strict safety standards,

and proposals for nuclear waste disposal be subjected to exhaustive examinations.

Research and Development

The development of solar energy equipment under this approach would be aggressively pursued as a major national

priority. The basic categories of projects

receiving support would be the same as

those discussed under Perspective B, but

funding would be given to a broad range of

projects, marketing programs would be accelerated, and emphasis placed on both

near-term and long-term approaches Part of

the price of an accelerated program, judged

to be acceptable because of the priority

given the undertaking, would be an increase

in funds wasted on designs which are eventually overtaken by better approaches. Proponents of this point of view argue that if

the United States were willing to make a

multi bill ion dolIar commitment to a project

to put man on the moon, a commitment of

similar size would be justified to develop

safe and reliable solar energy equipment.

Analysis

The incentives discussed in this perspective will, as expected, have a greater effect

in reducing the cost of solar energy perceived by solar equipment owners, and will

cost the Government more to implement.

Table I I I-2 indicates the impact of a group

of policies which consist of:

– A 20-percent investment tax credit,

–A 5-year depreciation allowed for all

solar equipment, and

– Exemption from property taxes

It can be seen

the effective cost

by 1.5¢ to 6¢/kWh

ISSUES

ISSUE 1

What changes in the Federal tax laws

would be the most effective in encouraging private investment in solar equipment?

that these credits reduce

of residential solar energy

How much would such policies cost the

taxpayers?

The tax laws can provide powerful incentives for the use of solar equipment without
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 7 5

Table ill-2.—The Effective Cost of Solar Energy in Residential Buildings

in Omaha, Nebr., [¢/kWh] With a High Level of Incentives

Direct

No Federal

Incentives Incentives* subsidy**

Solar hot water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0- 4.2 0.8-2.0 1.6-2.2

Solar heating and hot water. . . . . . . . . . . . . . . . . . . . . 3.0- 7.7 1.1-4.1 1.9-3,6

Solar heating and hot water with seasonal storage. . .

Solar heating and hot water with seasonal storage. . . 3.8- 6.9 1.3-2.9 2.5-4.0

Solar heating, cooling, and hot water . . . . . . . . . . . . . . 6.0 2.2 3.8

Solar photovoltaic electricity. . . . . . . . . . . . . . . . . . . . 3.8-11.8 1.2-5.7 2.6-6.1

——.

. Fd Incenl[ves consist of a 20 percent Investmen! tax credit, an allowed 5 year deprec[at[on schedule, and exemption

from property tax

“” This IS the effective cost of the subs!dy to the Government resultlng from the tax revenues because of the tax credits It IS

calculated assuming that the Government applies a 10 percent discount rate to future costs (See caveat In text )

Assu mptlr)ns 1985 startup of eqwpment

See volume II for detads of systems analyzed

the need for major Federal intervention in

the operations of the free market. Several

alternatives are possible:

1. A direct income tax credit. Such credits

wouId allow the taxpayer to subtract a

fixed fraction of the initial installed

cost of soIar equipment from his income tax Since these credits are deductions from taxes rather than from income, they wouId apply equalIy to al I

applicants provisions must also be

made so this program is fair to low income famiIies who are not now required to fiIe tax returns and to famiIies

whose tax credits exceed the taxes they

owe The effect of different types of tax

credits is iIIustrated in figure III-1.

Under existing laws, tax credits are

permitted for some commercial and industriaI equiprment, but not for investments in buildings, Nor are they allowed for heatlng, cooling, or other energygenerating equipment i nstaIled in

buildings However, a company that instaII such equipment in a buiIding it

does not own — and then selIs the energy produced –- wouId probably qualify

for a tax credit under present laws

2. Accelerated depreciation allowances.

Accelerated depreciation allowances

wouId be of greatest interest to corporations, utilities, and individuals in

high tax brackets. No individual is presently permitted to depreciate equipment in his own home, although equipment installed in the home by a company which sells energy could depreciate the equipment.

The effect of different types of depreciation schedules is illustrated in figure I I I-2,

Several observations can be made immediate y:

1. Permitting a homeowner to depreciate

the capital he invested in solar equipment over a period of 3 to 5 years

would reduce his effective capital

charges by about one-third Since institutional owners of energy-generating

equipment are permitted to depreciate

their equipment, the current tax policy

forbidding homeowners to do this has

the effect, if not the intention, of

discriminating against the ownership of

such equipment by the homeowner.

(This incentive would be of greatest

benefit to owners in high tax brackets )
76 ● Solar Technology to Today’s Energy Needs

Figure Ill-1 .— Effective Capital Costs as a Function of Investment Tax Credit

0.20

0,15

0.10

0.05

0.00

SOURCE: Office of Technology Assessment \

0 100/0
Figure lII-2.– Effective Capital Costs as a Function of Depreciation Schedules

0.20

0.15

0.05

SOURCE: Oftice of Technology Assessment

30 No

Depreciation

0.00

0 5 10 15 20

Depreciation Period (Years)

NOTES

( 1 ) The ~ffer tlve Interest rate paid on raplfal ‘ shown here Is the ratio between the ( apital related component of Ihe prlre percel~ ed by the consumer and the

total n I I J Ins tallerj P OSt Of the en~ rqy eq u I pme n t I n quest on Cap\ la I re Iated f. x penses I n I- Iude return on debt return on equ I ty (u n less 1 he equ I pment Is

I J w n~d by the homeowner) la XPS ( w t h al I [~w an ces for d epr~~ iat Ion and (~t h er w rl tc offs) and Insurance

(2 I Th~ t>asf, II n e assumpl I I ns and fh r? Ie[ h n Iq ues used fc f,~]m pute th c data sh, w n {In t h IS f q u re are dI sc ussed I n detal I I n the r hap fer on Analy I I ral Methods ‘‘
78 . Solar Technology to Today’s Energy Needs

2. Commercial, industrial, and utility owners can also be strongly influenced by

altering policies on deductions for depreciation. In the cases shown in figure

III-2, real estate investors, who expect a

10-percent return on their capital after

taxes can reduce their capital-related

costs by over one-third if they are permitted to depreciate equipment rapidly. The effect is even greater for an industrial owner expecting a 20-percent

rate of return.

PROPERTY TAXES

Property taxes can add as much as 10 to

25 percent to the cost of solar energy. The

taxes, of course, are imposed entirely by

States and municipalities and vary greatly

around the country (see table 11 1-3). I n some

urban areas in the northeast, for example,

taxes are so high that an investment in onsite solar equipment would be prohibitively

expensive for many individuals and companies. Figure I I I-3 illustrates the substantial

effect of removing a “typical” property tax

since, in most cases, the tax increases the effective investment cost by nearly 10 percent.

Some problems may arise concerning the

property taxes paid by utilities and other

organizations if they own solar equipment.

Because in many cases these organizations

pay taxes at much higher rates than those

paid by individuals, there would be a disincentive to invest in solar equipment.

Whether this is desirable must be decided.

Another decision is whether to exempt companies which manufacture solar equipment

from property taxes. There might also be

some confusion about charging the property

taxes in a case where a utility or other

private concern places equipment on a

house or building and charges the building

owner for the energy produced.

Property taxes are not imposed by the

Federal Government and therefore cannot

be removed with Federal legislation. It may

be possible to use Federal programs to encourage local governments to remove property taxes, perhaps by agreeing to compensate them in some way for lost revenues attributable to solar property tax exemptions

or to penalize States which do not reduce

property taxes by withholding Federal solar

subsidies. The National Energy Plan proposed by the Administration states that it

Table III-3. —Property Tax Rates in Selected U.S. Cities

Residential Property Tax Rates in Selected Large Cities: 1974

Effective Tax Effective Tax

Rate per $100 Rate per $100

City Rank Rate City Rank Rate

Boston. . . . . . . . . . . . . . . . . . . . 1 $5.94 New York City . . . . . . . . 16 $2.18

Buffalo . . . . . . . . . . . . . . . . . . 2 4.31 San Francisco . . . . . . . . . . 17 2.13 ,– OTA

Milwaukee . . . . . . . . . . . . . . . . 3 3.63 Cleveland . . . . . . . . . . . . . 18 1 88 Baseline

Los Angeles . . . . . . . . . . . . . . 4 3.43 Seattle. . . . . . . . . . . . . . . 19 1.82 assumption

San Antonio ., . . . . . . . . . . . . . 5 3.43 St. Louis . . . . . . . . . . . . . . . 20 1.80 $200

Indianapolis . . . . . . . . . . . . . 6 3.29 Memphis . . . . . . . . . . . . 21 1 77

Baltimore . . . . . . . . . . . . . . . . . 7 3,24 Denver . . . . . . . . . . . . . 22 1,71

Pittsburgh ... . . . . . . . . 8 2.82 Jacksonville . . . . . . . . . . 23 1. 69

Philadelphia. . . . . . . . . . . . . . . 9 2.80 New Orleans ., . . . . . . . 24 1,69

Chicago. . . . . . . . . . . . . . . 10 2.75 Kansas City . . . . . . . . . 25 1,57

Detroit . . . . . . . . . . . . . . . . . 11 2.73 Phoenix. . . . . . . . . . . . . . . . 26 1.55

Dallas . . . . . . . . . . . . . . . . . . 12 2.60 Washington, D.C. . . . . . 27 1.54

Houston ., . . . . . . . . . . . , . . . . 13 2.38 Nashville . . . . . . . . . . . . . 28 1 39

Atlanta . . . . . . . . . . . . . . . . 14 2.24 Cincinnati . . . . . . . . . . . . . . 29 1.31

San Diego. ., . . . . . . . . . . . 15 2.23 Columbus . . . . . . . . . . . . . 30 1.17

SOURCE: Government of the Dwtrict of Columbia, Department of Finance and Revenue, Tax Bj}rdens (n Wash InrItnn DC Corn

pared wlfh Ma/or Stafe and Loca/ Tax Burdens in the Naf/on’s Thirty Largest C/t(es 1974.
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 79

Figure lll-3.— Effective Capital Costs With and Without Property Taxes

0.20

0.15

0,05

0.00

NOTES

( 1 I The ‘e ffertlve !nterest rate paid on raplfal’ shown here IS the rat(r) bet ~ eon th(> “a~~i!al related -omponf>nt {~f thf prl L e ~er elved by the consumer and the

total n I t al Ins fal led , r,st (of I he energy {,q u p men t I n quest Ion Ca ~, tal r(,lat~,l P x pen SPS n{- I u~e return [~n debt return on equ I ty (U nlf?ss lh~ eq [J I preen t Is

ow n~d by the n om~c w n Pr) !a k Ps (w It h al I o wancps for deprc - !at l~)rl and r)th ~r t+ rl tP o ffs J and I ns u ran~e

(2) Thf bas~>ll nf assumpt JrJS and th~ tf hn q ues use(j t ) Jnl FJ u Ie !h r, dala sh j N rI , !n 1 h IS f q u re dre d ISr USSL ‘~ I n deta I I n I he I ha~j te r on Anal y t I al M~t hods

SOURCE Off Ice of Technology Assessment
80 . Solar Technology to Today’s Energy Needs

would be desirable for the States to exempt

solar devices from property taxes, and

several have already done so.23

SALES TAXES

Sales taxes also lie beyond the Federal

sphere, but they, too, can present an impediment to the installation of solar equipment.

Here again, the rates for sales taxes vary

from State to State. In Connecticut it is 7

percent, in Nebraska it is 2.5 percent, in New

Hampshire there is none.4 Removing the tax

from sales of solar equipment would be of

some benefit in reducing initial costs. However, an exemption would not have as great

an effect as the property tax exemption

which must be paid each year.

The Cost of Tax Incentives to the Government

The cost to the Government of changes in

tax policy can be computed from the data in

figures II l-l and II I-2 if it assumed that the

Government and the private investor use the

same discount rate (see volume 11, chapter

l). This is done by finding the difference between the “effective cost of capital” which

would apply with and without the change in

policy. For example, if the effective interest

rate paid on capital applied to a real-estate

investor is 10.6 percent without a tax credit

and 8.6 percent with a 20-percent credit, the

average annual loss of revenues to the Government during the Iife of the equipment is

simply 2 percent of the initial cost.

ISSUE 2

Will difficulties in obtaining loans hinder the

installation of onsite solar-energy equipment? If so, can Federal authority to regulate

the mortgage reduce such problems?

‘The National Energy Plan, p 76

‘National Bureau of Standards, Survey of State

Legislation In Solar Energy

‘The World Almanac and Book of Facts 1977,

Newspaper Enterprise Association, I nc , Cleveland &

New York, p 105

SUMMARY

The short answer to the first question is:

probably, at least for a while. Banks and

other Iending institutions are understandably reluctant to invest in mortgages for

residential buildings that plan to use costly

new energy equipment with unproven market value, since they might not be able to

recover the value of such loans i n a foreclosure sale. They are similarly reluctant to

provide funding for commercial and industrial equipment if the owner cannot convince them that the system wilI produce a

favorable cash flow during the period of the

loan. Present statistics about the marketability and performance of most types of

solar energy equipment are inadequate to

support actuarialIy sound decisions, and

few prospective lenders appear to have seen

what little information is now available.

Although solar devices with proven characteristics can be expected to gain gradual acceptance in the lending industry, the question of whether the Government can or

should accelerate this process has not been

resolved.

The Government has successfully used

loan guarantee and mortgage insurance programs in the past to induce private lending

institutions to provide funds for projects

deemed socially desirable; Federal Housing

Administration (FHA) and Veterans Administration (VA) have made loans available to

prospective homebuyers for decades. The

Government is also in a position to alter current banking practices through the great

variety of regulatory and secondary mortgage institutions which operate under Federal charter, The potential for using these

organizations to stimulate loans for solar

programs is discussed below,

THE PROBLEM

In the absence of adequate informatio n

on the reliability, lifetimes, and marketability of soIar equipment, many banks are reluctant to include solar devices in the value

of mortgages made on residential buildings.

In a recent survey by Regional and Urban

Planning Implementation, Inc. (R UP I), 63
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 81

percent of the lending institutions interviewed Indicated that they would “exclude

the excess cost (of solar equipment) from

the appraised value of the house” for loanmaking purposes, and an additional 22 percent indicated that they would lower the

loan-to-value ratio of the loan. 5 The average

loan actualIy issued by the institutions interviewed covered 55 percent of the vaIue of

the solar devices. ’ (However, the institutions

felt that it solar devices were deemed to be

an actuarialIy sound investment, they would

lend funds for the devices at the same rates

they charged for other types of buiIding

loans. ) Most of the solar loans were issued

for expensive custom-built homes, and in

many cases the owners or builders had an

established relationship with the lender. 7

This reluctance to issue loans for solar

devices is accentuated both by the fact that

most banks are simply unaware of the informat ion gathered about solar equipment,

and by the tact that very few lending institutions take energy costs into account when

determining the abiIity of a prospective borrower to meet mortgage payments.

Most Iending institutions do not include

an applicant’s projected energy biIIs in an

assessment of his abiIity to meet mortgage

payments But this practice is changing.

Forty percent of the lending institutions interviewed in the RUPI study indicated that

since 1973 energy considerations had influenced lending decisions “a great deal” or

had become “critical” in lending decisions,

and 50 percent stated that the importance

of energy in these decisions would increase.8

Most banks rely primarily on the principal,

interest, taxes, and insurance (PIT I) evaluation technique, which compares a prospective borrower’s income before taxes to the

PIT I costs which he must bear to support his

‘Keglonal and Urban Pldnning Implementation Inc

(R UP I), Home Mortgage Lend/ng and So/ar Energy,

February 1977, p 13 (Prepared for the Divlslon of

Energy, Bulldlng Technology and Standards, Otflce of

POIIC Y Development and Research, HUD )

‘Ib{d , p 99

‘I bld

8RUPI, p 52

investment i n a home. Since the borrower is

equally committed to carrying the energy

costs of his home, there has been speculation that the PIT I formula may be expanded

to include energy costs (although this is not

now a common practice).

Lack of information about home energy

consumption and the value of solar equipment makes it difficult for institutions to

evaluate energy costs, even if they have a

desire to do so. Only 9 percent of the lenders

interviewed in the RUPI study had seen estimates of solar energy savings, only 4 percent

had seen cost benefit analysis for solar

equipment, and only 9 percent had seen an

installed solar device or plans for an operational system. 9

THE EFFECT OF MORTGAGE

POLICY ON SOLAR COSTS

The availability of financing can present a

major barrier to rapid introduction of solar

equipment. The effects of loan-to-value ratios on overall capital costs are shown in

figure III-4 and the effect of changing interest rates is shown in figure I I I-5. The

results require some interpretation:

— From the perspective of a present value

anaIysis, the fraction borrowed has

relatively little effect on the capital

costs perceived by the homeowner,

given the assumption that the owner

uses a 10-percent discount rate to

evaluate future costs. This is because

the discount rate chosen in the calculation is close to the interest rate charged

for the loan. The fraction borrowed can

have a much greater effect than figure

1 I I-4 indicates, however, since the requirement for a large downpayment

can be a prohibitive barrier.

–The fraction borrowed strongly affects

the prices which must be charged by industrial firms and, to a lesser extent, the

prices charged by the hypothetical real

estate investor. This is simply due to the

fact that the investors expect a much

‘RUPI, p 61
82 ● Solar Technology to Today’s Energy Needs

Figure ill-4.—The Effect of Loan-To-Value Ratios on Overall Capital Costs

0.40

0,35

0.30

0.25

0.20

0.15

0.10

0.05

SOURCE: Office of Technology Assessment

0.00

0

P.U. = .142

M.U. = .095

.25 .5 .75

Fraction Borrowed

1

NOTE

The baseline assumptions and the techniques used to compute the data shown on this figure are discussed In detail In the chapter on “Analytical Methods “
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 8 3

—

Figure ill-5.—The Effect of Interest Rates on Overall Capital Costs

0,20

0.15

0,05

SOURCE: Office of Technology Assessment

0.00

0 2 4 6 8 10 12 14 16 18 20

Interest Rate on Loan (O/. )
84 ● Solar Technology to Today’s Energy Needs

higher return on their capital than the

interest rates assumed for the loan.

— Interpretation of the effect of interest

rates on loans is straightforward. The

policy issue raised here is one of finding

a way to persuade lending institutions

to risk investments in solar equipment.

Figure I I I-6 shows the results of a recent

survey of the reaction of a number of lending institutions to a number of proposed

policies. It is apparent that the lenders are

not interested in tax incentives which assist

potential owners. They are much more interested in performance certification of the

devices and in Federal insurance and secondary markets for mortgages.

Many existing Federal programs insure or

subsidize loans to promote objectives

deemed socially desirable. These programs

are discussed in the following section. How-.

ever, one difficulty with a policy that creates such distortions in the loan market is

that the implicit subsidies are extremely difficult to calculate, Encouraging the use of

capital in one area necessarily removes the

capital from other applications; thus, it is

never clear who, if anyone, suffers as a

resuIt.

Another option for encouraging lending

institutions to make financing available to

potential owners of solar equipment would

be to find some way of requiring lending institutions to include estimates of the borrower’s ability to cover utility costs in the

process of estimating the borrower’s ability

to pay back the loan. This type of analysis

might often benefit solar equipment owners.

Several techniques for doing this are discussed.

A SOLAR LOAN PROGRAM

A program which made loans more attractive to potential solar customers would have

several generic advantages over tax incentives:

1, They avoid complicating the tax laws.

Recent tax reforms have attempted to

separate Government incentives pro2.

3.

4.

grams from the revenue-raising function of the Internal Revenue Service.

The benefits of a subsidized loan may

be easier for a prospective buyer to understand and its impact is more immediate. It is apparent that consumers

of solar energy equipment must be persuaded to make purchases on the basis

that their net monthly payments for

energy will be lower if they install solar

energy equipment. It is easier to make

comparisons between conventional and

solar billing when loan incentives are

provided.

A tax rebate requires owners to tie up

their own capital while waiting for a refund. This wait can create real financial

difficulty and the delayed gratification

can have a psychological impact reducing the attractiveness of the incentive.

It may be easier for low-incom e

families to take advantage of a loan

program which requires a relatively

small downpayment, for example, than

a program which requires negotiating

loans from conventional sources. It is

interesting to notice that loan incentives may be more attractive to lowincome homeowners than to homeowners with large incomes. Families in

high-income tax brackets pay a lower

effective interest rate since interest is

deductible, and would therefore not

benefit as greatly from an incentive

which lowered the interest rates and

hence their deduction.

If it is possible to place the loan as a

part of a mortgage package used to

finance an entire building or house, it

may be possible to reduce the cost of

administering the program and appraising the solar equipment. If tax programs

are used, the IRS must presumably find

a way to make independent audits of

the projects.

Loan programs, of course, are not without

problems. They can be complex and costly

to administer, particularly if it is necessary

to establish a separate bureaucracy to over-
Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy . 85

Figure lll-6.— Lender Perceptions of Likely Impact of Incentive Options on Loan Decisions

Percentage of Lenders Indicating Incentive

Would Have “Substantial Impact” or Be

“sufficient To Make Loan”

Type of Incentive Program

1. “Conversion” Insurance

2. Certification of Solar Energy

Systems

3. Top Part of the Risk Insurance

4. Secondary Market Eliglbility

(FHLMC, FNMA)

5. GNMA Purchase with Lender

Servicing

6. FHA/VA Eliglbility with Higher

Mortgage Limits

7. Value Protect Ion Insurance

8. Local Property Tax Exemption

for Added Cost

9. (For Multi-Family) Accelerated

Deprectation

10. Subsidized Interest Rates

11, Income Tax Credit for 1st Costs

(or Investment Credit)

12. “Public ” 2nd Mortgage Loan for

Extra Solar Costs

13. Linked to Special Feature—

(e.g., Variable Interest Rate,

Balloon, etc.)

SOURCE RUPI CIp .[1
86 ● Solar Technology to Today’s Energy Needs

see the operation of the program. Lending

institutions constantly complain about the

amount of paperwork required by Federal

regulatory authorities and this paperwork

can contribute significantly to the cost of a

loan. Since the costs of paperwork are nearly Independent of the size of the loan, loan

subsidies may not be an detractive technique for encouraging the installation of

solar equipment costing less than $1,000 to

$1,500. In these cases, it is much more likely

that the purchaser will be able to make a

single payment for the equipment and a

direct grant or tax credit would be easier to

administer.

There has also been some concern about

loan support programs which commit the

Government to administering programs over

a term of many years.

The significance of all of the problems

cited here depend on the details of how the

loan program is administered. Concern

about long-term Federal commitments can

be reduced, for example, by simply having

the Government make a single payment to a

lending institution which would administer

the loan, to cover the difference between

the return received from a subsidized and a

commercial loan.

If the Government uses an 8-percent discount rate (roughly the current cost of longterm Government bonds) a 3-percent loan

covering 95 percent of the cost of a solar

system owned by an individual homeowner

has roughly the same effect on average

monthly costs as an investment tax credit of

34 percent. If the system is owned by the

owners of an apartment building, the loan

would be equivalent to a credit of about 62

percent. The Government cost associated

with the loan program for homeowners

would be about the same as that for an investment tax credit of 29 percent (assuming

no loan placement fee).

EXISTING FEDERAL LOAN PROGRAMS

The Federal Government has a great variety of programs for subsidizing and regulating the U.S. financial community. These

fall into the following categories:

1.

2.

3.

4.

5.

Direct Federal loans and programs

which subsidize the interest paid to private lending institutions;

Programs which “guarantee” loans with

a contract in which the Government

agrees to purchase a mortgage offered

by a private investment company if the

borrower defaults (typically the debtor

is then still Iiable to the Government for

the outstanding funds and must either

sell the property or permit the Government to sell it for him);

Loan “insurance” programs, in which

the Government charges the borrower a

smalI annual fee and agrees to reimburse the lender in the event of a default;

Federally chartered but privately

owned “secondary mortgage” institutions, which purchase mortgages from

primary lenders in order to free the

funds of these lenders for further mortgages; the Federal National Mortgage

Association can borrow funds directly

from the Federal Treasury; and

Regulatory institutions which oversee

the operations of banks, savings and

loan institutions, and other lending

organizations,

Each of these programs and organizations

could retard the installation of solar equipment or, if Federal leverage is applied, accelerate it.

Direct Federal Loan Guarantees for Buildings

Most direct Federal loans are issued to

projects designed to serve low-income

groups–urban housing projects, hospitals,

homes for the aging–although some funds

are available for experimental communities

and new energy equipment. Any direct loans

for solar equipment will have to compete

with their use for urgent social programs. It

may make sense to increase funding in these

direct-loan programs to reduce dependence

on long-term Federal support for operating
Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy . 87

—

costs (see discussion in the previous issue),

The major direct-loan programs are:

Programs Administered by the Department

of Housing and Urban Development (HUD).–

1) Public Housing: The Housing Act of 1937

(section 5) permits the Federal Government

to directly finance housing for low-income

families and the elderly through federally

guaranteed municipal bonds. Additiona l

funds are allocated each year to allow

“modern i z at ion” of existin g structures

These programs do not have specific goals

for energy conservation, although the properties must meet certain minimum HUD

standards. Energy conservation features

couId be included in these standards.

(2) Housing for the Elderly and the Handicapped: Section 202 of the Housing Act of

1959 provides loans for nonprofit sponsors

of new or substantialIy rehabiIitated rental

housing for the elderly or the handicapped.

The program also has no standards specificalIy designed for energy conservation. The

projects constructed under this section,

however, tend to be initiated by experienced

and sophisticated managers, contractors,

and architects, who are more likely to be attracted to novel energy systems than are the

builders of public housing projects, which

have been plagued by cost overruns, defaults, and tenant problems,

Programs Administered by the U.S. Department of Agriculture (USDA). — The Department of Agriculture has two large Federal

loan programs for low- and moderate-income rural families that could have applications for solar technology.

The first is a new conservation program

under the Farmers Home Administration

(FmHA), a $500 million to $1 billion project

announced on February 28, 1977. Under this

program, customers of electric cooperatives

can receive 8 percent loans, repayable

through their monthly electric bills, for such

conservation measures as weatherization,

storm window and door instalIation, and instalIation of attic cans, to a maximum expenditure of $1,500 a family. No new Federal appropriations or authorizations were

necessary for this program; the money is left

over from the FmHA’s Section 502 homeconstruction loan program. But the conservation guidelines do not permit structural

work, thus precluding solar installations. No

legislation would be necessary to change

the regulations; it could be done administratively within the Agriculture Department

The second large program is the Rural

Electrification Administration (REA) loan

program to electric cooperatives. There are

two parts to this program — a direct loan authority of $75 million to $900 million (in FY

76) to cooperatives for electric distribution

and transmission faciIities. This program

would appear to have no solar applications.

However, a second REA program would. It is

an open-ended REA loan-guarantee program, again to co-ops, for construction of

electric generating faciIities.

These loans, at prevailing interest rates,

are made by a commercial bank or, more

commonly, through the Federal Financing

Bank within the Treasury Department. In

calendar 1976, such REA-guaranteed loans

totaled $3.7 bill ion,

There are no restrictions, either under the

law or under REA regulations, as to what

type of electric generating facility may be

made with the REA-guaranteed loans. Thus,

a solar electric generating plant could qualify for such a loan – at least so far as REA is

concerned — assuming that the lending institution and the local electric co- operative

conclude that the solar installation would

be cost-effective.

The two largest impediments to using this

large Federal program to foster the solar

market would seem to be (a) the need for a

backup system (a small diesel generator

could suffice) and (b) the problem of convincing banks and co-op officials that a

solar generating facility would be practical

(when it is possible to make such a case).

REA officials stress that their agency’s mission is not to experiment with new or novel

technologies, but to provide electricity to

rural customers at the cheapest possible

rates.
88 . Solar Technology to Today’s Energy Needs

Programs Administered by the Small Business

Administration (SBA).– The SBA has funds

available for subsidizing loans to qualifying

smalI businesses. These funds might be useful to firms manufacturing or installing solar

equipment, since such firms tend to be quite

smalI.

Loan Guarantees

Veterans Administration (VA).– The Serviceman’s Readjustment Act of 1944 allows

the VA to guarantee loans to qualifying

veterans for residential buildings with one to

four units. The program guarantees about

350,000 units a year, The loans can be made

for any amount and cover 100 percent of the

value of the property. There are no energyconservation requirements, although the VA

will only insure property which meets “minimum property standards” established by the

FHA.

Federal Energy Administration (FEA).–The

Energy Conservation and Production Act

provides loan guarantees for a wide range of

conservation and solar energy equipment.

Regulations governing the application of the

funds were still being drafted in mid-1977.

HUD Loan Guarantee Programs.–Amendments to the Housing Act of 1968 authorize

HUD to make loan guarantees for privately

developed new towns and for a variety of

community facilities. To date, the program

has extended guarantees to 13 new towns,

some of which have projects for solar heating and cooling funded under the ERDA/-

HUD solar heating and cooling demonstration program.

Mortgage Insurance

The Housing Act of 1934 established the

Federal Housing Administration (FHA) and

the FHA Insurance Fund to allow families

with low and moderate incomes to obtain

mortgages at reasonable rates, The program

has since expanded to include apartments,

cooperatives, nursing homes, and group

‘

[) F’ubl IC Ldw 94-385, Title IV, section D

‘ ‘Title IV of the Hou\lng Act of 1968, amended as

Title VII of the Housing Act of 1970

medical practice facilities, The insurance

program collects premiums from borrowers

and provides a fund to reimburse lenders in

the case of defaults. The value of interest

rates allowed for FHA-insured loans varies

and has recently been below the rate

charged by the private mortgage insurance

companies. In 1977, home-purchase loans

financed under Section 203b charged 8-

percent interest; home-improvement loans

under Title I charged 12 percent.

FHA’s direct participation in the mortgage market is diminishing. It now insures

only about 17 percent of the loans made on

1- to 4-unit nonfarm residential buildings.

The program is still extremely influential,

however, if only because of the standards it

sets for residential structures. All older

homes purchased with FHA insurance must

be appraised by the FHA and receive a “Certificate of Reasonable Value, ” which forms

the basis of the loan amount. New homes

can be insured only if they meet FHA’s

“minimum property standards, ” As noted

earlier, these standards form the basis for

many other Federal loan programs. They are

also widely used by private lending institutions as the standards of value. Builders

designing low-cost housing have, in many

cases, chosen to meet these standards,

since housing quality that did not measure

up to them would have reduced the avail ability of financing for potential buyers.

The FHA standards reflect both the quality of the construction and its marketability.

No firm policy has been established for

solar-energy devices, although a 1974

amendment to the FHA law permits the use

of FHA loans for solar equipment (The

amendment may have been unnecessary, as

FHA loans were used during the 1930’s to

purchase solar water heaters in Florida. )

Current FHA solar standards of performance quality employ the National Bureau of

Standards “ Interim Performance Criteria”

for solar devices. ” The major difficulty,

“RUPI, p 133

1‘FHA document FPMC-FHA, dated February 19,

1976
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy . 89

however, will not be the quality of the

equipment but whether it wiII contribute t o

the resale value of the house. FHA is particularly sensitive on this point, since it

deals primarily with low- and middle-income

families to whom initial housing costs are

important, A recent FHA publication noted

that in inspecting property with solar

devices, “[the] field office must also determine that a ready market exists for the property with the increased cost of the solar

equipment." 14 An applicant faiIing to obtain

FHA certification for a solar device has the

right to a hearing before the local FHA office The results are difficult to predict and

wi II doubtlessly depend on the officials’

familiarity with costs and benefits of solar

equipment. Failing to obtain a direct FHA

loan, the applicant has the option of utilizing a H U D “ Experimental Housing Program

(Section 233). ”

HUD’s experimental housing program is

designed to provide an incentive for the construction of innovative or unconventional

housing systems that do not meet the conservative standards of the FH A certification

processes. The program’s larger purpose is

to develop familiarity with experimental

designs that will provide the basis for altering the FHA standards.

15 Unfortunately, influence of experimental programs on traditional housing has not been notable thus far,

Loans for home improvement and mobile

homes insured under Title I do not require a

preinspection, although FHA audits projects

after loans are granted. Up to $7,500 can be

obtained without security.

The proposed National Energy Act would

amend the act establishing these loan guarantee programs in three ways:

1. Section 110 would add public utilities

to the types of institutions which can

place loans for energy-conservation

equipment insurable by FHA.

14 FPMC-FHA 76-8

150rvjlle Lee, D/rector of HUD’s SectIon 233 program$, private communlcatlon, 1977

2

3

Section 111 clarifies the definitions for

energy-conserving equipment and solarenergy devices.

Section 112 provides an opportunity to

use Title I funds for experimental

energy equipment but at higher interest

rates than those conventionII y

charged for home improvements, Actual rates would be determined by a

study conducted by the Secretary of

HUD.

Federally Chartered Secondary. Mortgage Institutions

Many of the mortgages issued for residential buildings in the United States are not

held by the primary lending institution for

the full mortgage period. Instead, they are

sold to organizations which are more interested in holding notes over a long period

and which use the primary lenders as agents

to acquire them. Selling mortgages to a

secondary-mortgage institution frees the

assets of the primary lender, who is then

able to use these funds to issue further mortgages. The Federal Government sponsors

two of the largest purchasers of secondary

loans: the Federal National Mortgage Association (called “Fannie Mae” by generations

of brokers unable to pronounce FNMA), and

the Federal Home Loan Mortgage Corporation (alias “Freddie Mac”).

Primary lenders are critically interested in

ensuring that their loans will be repurchased

by these organizations. If the secondarymortgage institutions are negatively inclined toward solar equipment, this could

affect the willingness of primary lenders to

approve loans involving such equipment.

According to the RUPI study cited earlier,

both FHLMC and FNMA have indicated that

“until solar systems achieve some degree of

market acceptance, they may conclude that

incremental first costs should be largely,

perhaps even entirely, excluded from the

mortgageable value for the purpose of their

programs,’” The manager of FNMA appraisals was quoted as saying that if “people

“Title 12 (Banks and Banking, subchapter I I 1,

171 6a)
90 Ž Solar Technology to Today’s Energy Needs

wish to experiment they should do so with

their own money, not someone else’s."17 

On the other hand, the quasi-public nature of these organizations makes them susceptible to public-policy guidance.

The Federal National Mortgage Association was established by Congress in 1934 to

“provide supplementary assistance to the

secondary market for home mortgages by

providing a degree of liquidity for mortgage

investments, thereby improving the distribution of investment capital available for

home mortgage financing” and to provide

special assistance for special purposes. It

purchased about $7 billion in loans in

1974. 18 It raises funds by private subscription, but has “backstop” authority to borrow directly from the Federal Treasury. Five

of its 15 board members are appointed directly by the President of the United States,

Fannie Mae can purchase loans guaranteed

by FHA or other institutions [section

1717(b.1 )] at full value. It can also purchase

conventional uninsured loans, subject to restrictions on the loan-to-value ratio and

other limitations [section 1717(b.2)]. About

85 percent of its loans are purchased from

mortgage bankers.

The FNMA tends to place great reliance

on the judgment of primary lenders, and as a

result, its lending policies tend to be determined by the values of the mortgage banking industry.

The Federal Home Loan Mortgage Corporation operates under the auspices of the

Federal Home Loan Bank Board (FHLBB)

and primarily serves savings and loan institutions. The Corporation purchased approximately $1.5 billion in loans in 1974.

The members of the board of the FHLMC are

appointed by the FHLBB, who in turn are appointed by the President. The Corporation

acts under regulations established in the

Federal Home Loan Bank Act, It raises

‘ ‘Barrett, Flnanclng the Solar Home, NSF Grant

APR 75-18360 (j une 1976), p 141

‘

a Barrett, op cit., p 139

“Barrett, Financing the Solar Home, NSF Grant

APR 75-18360 (June 1976), p 139

funds, entirely by subscription, from the institutions it services. The FHLMC’s regulations place more risk on the primary lenders.

For example, the FHLMC can require the

primary lender to take back a repurchased

loan if irregularities are discovered.

The proposed National Energy Act would

amend the charters of both the FHLMC and

FNMA, to make it clear that funds can be

used for loans for “energy-conserving improvements to residential real estate.” 20

Solar devices are not explicity mentioned,

but their inclusion may have been intended.

Regulatory Authority

Nearly 97 percent of all loans granted in

the United States are issued by lending organizations subject to some kind of Federal

regulation. Savings and loan associations,

for example, are tightly controlled by the

Federal Home Loan Bank Board. The Federal Deposit Insurance Corporation regulates

mutual savings and commercial banks. Neither appear to have a specific policy for encouraging or discouraging energy-related

loans.

ISSUE 3

Can purchases of solar equipment for Federal buildings be used to stimulate the solar industry?

A major program for installing solar

equipment on Federal buildings could be

one of the Government’s most powerful

tools for encouraging the development of

mass production of solar equipment by private industry.

Consider the following:

● The Federal Government owns or leases

approximately 446,000 buildings in the

United States, with a combined floor

area of nearly 3 billion square feet and

was spending almost $1.7 bill ion annually by mid-1977 to heat and cool

them. (That figure was expected to

‘OTltle 1, sections113 and 114
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy Ž 91

reach $1 9 billion by the end of 1977 ,

and about $3.5 billion by 1985, ) If 10

percent of the present heating/cooling

costs were capitalized — used for debt

payments for the purchase of solar

equipment — the Government could

purchase nearly 100 million square feet

of solar coIIectors annualIy. *

● The Federal Government subsidizes

operating expenses, including heating

and cooling costs, of a large number of

projects built with Federal assistance.

The Department of Housing and Urban

Development alone paid more than

$575 million in 1977 to subsidize the

operating and energy bilIs of the nearly

1 million units of public housing administered by subsidized local housing

authorities If 10 percent of this were

capitalized, the Government could support the purchase of nearly 30 million

square feet of colIectors annualIy.

Ž It wouId be difficuIt for the Government to encourage private concerns to

instalI solar equipment if it is not using

solar equipment on its own buildings.

In spite of the enormous potential, Federal programs for purchase of solar equipment

have been proceeding quite slowly, largely

because of concern about the cost effectiveness of solar devices. This concern is

often magnified by the inability of program

administrators to accurately evaluate the

costs of solar techniques, I n some cases, required formulas for determining the worth

of a Federal investment (i. e., fixed Iimits on

building costs, and present value computations with high discount rates) have inhibited these programs.

The opportunity to use Federal buildings

for experimental energy equipment raises

three difficult but important questions:

1. What should the Government use as a

“discount rate” to evaluate alternative investments?

‘Assuming $20 per square foot for an Installed system

There is a considerable amount of

disagreement among analysts on this point

Some argue that the Government should

make decisions with the same expectations

of return as private investors This view was

formalized in a ruling by OMB, which held

that the Government should only invest In

equipment which wouId resuIt in a 10-percent return on investment since this rate

“represents an estimate of the average rate

of return on private investment before taxes

and after infIation.” 21 Others argue, however, that the free market does not necessarily accurately assess the social costs of

investments and that the Federal Government shouId therefore use investment criteria which better reflect social costs. Even

if this basic principle is accepted, however,

it becomes extremely difficuIt to determine

what economic expectations are proper Investments must be assigned values based on

concerns about the environment, social

costs, benefits to labor, benefits to national

security, the stability of resource supplies,

and other criteria difficult to evaluate in

conventional economic terms

When the Government makes an investment that pays less than the return which

could be realized if invested in the free

market, society is losing some of the value

of that capital. This of course means that

society is subsidizing the investment In

some way. The exact amount of this subsidy,

however, can be as difficult to quantify as

the value society might realize from the investment.

Nonetheless, several discount rates can

be used to evaluate Federal equipment purchases:

●

●

10 percent rate of return after taxes and

before inflation: this technique would

result in Federal investments in solar

equipment which neither lead nor lag

investments made by private industry.

Use of a rate of return equal to the rate

of the growth of the U.S. GNP: this

“George P Shultz, “Discount Rates to Be Used In

Evaluating Time-Dlstrlbuted Costs and Benefits, ”

OMB Circular A-94, Mar 27, 1972
91 Ž Solar Technology to Today’s Energy Needs

●

would encourage Federal purchases of

solar equipment and ensure that funds

extracted from the economy by th e

Government were not affecting overall

economic growth. (This would imply a

real discount rate of 2 to 5 percent. )

Require only that the Federal Government recapture its initial investment

without earning a return on the funds:

this would obviously be a stronge r

stimuIus to Federal purchase of the

equipment. (Zero percent discoun t

rate. )

The effect of applying different Federal

discount rates to prospective Federal investments is iIlustrated in figure III-7; the anticipated effects of three separate discount

rates on Federal decisions to purchase energy equipment are shown in figure I I 1-8.

Figure ill-7.—The Effective Cost of Capital to the Government as a Function of the

Discount Rate Used in Decisionmaking

(Assumptions methodology used in preparing this figure are discussed in detail in

volume 11, chapter 1)

020

9

SOURCE Of f(c e of Technology Assessment

15
Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy ● 93

Figure Ill-8.—The Effect of Federal Discount Rate on the Perceived Cost of Federal

Investments in Three Types of Solar Installations

(in $/month/unit in a 196 unit high rise apartment)

12J s[jldr hratl n q a no h I t w a tc r systf-m uses 4100 m2 of flat @df(, r olle[ tors w h I h 2 r~sl 196 $Imz Installed (near term prII es) and 1 2 mtlllon k ~ h I(}v. temperatu rf

t h c r{Tl al SII ~ raqe ~ s{a> Jn al I n u ndf, rq ro u nc Ian ks

(31 s Id r ,.{{. tr # 1 b C,(, S 2500 m 2 ~f t ~ o ax Is t rdr k mq I f~lle tf~rs w I f h GaAs phO!u vol Idl( . el Is The c olleI t{]rs f OS! 102 $ ‘m 2 I n stall e[~ In- IU d !ng I R IS (an [I

1 I rr~ I \ 1 I es! nla te (Jf fu I(J re pr! I.es I 10000 k w h fjf low Ie m pc>ra tLJ re thermal st( I rdqf> no batlerles are used

(4) solar CIICI trl #2 uses 4263 m 2 of one ax Is t rar k I n 9 ~ [ III(J 1 Jr \ w,! h s II I Jn ~h{ I(J Y olt al I el Is The -7,11 [~1 tci rs I- ost 300 $fm2 I n c I L d n q t he - f]st o I the 15000

$1 ~~cak k w ) the sysl e m has 17000 k w h of low tern pera! u r{, t h ermal sto ragf all d n J bat t (rles

n

assumes 1976 start u [J ~ ost an\ ~, ler ! r I r prj PS n reas I n q al~~nq BN L f( J re a~fs

m

\ assumes that electrlc prtces Increase by a factor of 5 over 60 = years (In constant dollars)

2. If it is determined that the Government

should subsidize the market in novel energy equipment, how should it select

equipment?

If it is assumed that the Government will

purchase equipment which cannot be justified in traditional economic terms, values

other than those used by the free market

must be applied This is a perilous undertaking since it runs the risk that the bureaucracy wilI select equipment which would not

have been chosen by the market if it had

been given time to develop along traditional

lines, In extreme cases, mistakes might actually result in slowing the rate at whic h

solar equipment enters the market if the

Federal stimulus results in accelerating the

instalIation of less desirable devices,

thereby diminishing interest in promisi ng

alternatives. At a minimum, any Federal procurement program must be carefulIy integrated with an overall plan to promote a

market for solar equipment as discussed in

the section reviewing overalI policy alternatives.
94 ● Solar Technology to Today’s Energy Needs

3. What future fuel prices should the Government assume when evaluating the

cost-effectiveness of solar technologies

for specific applications?

THE POTENTIAL OF INDIVIDUAL AGENCIES

Department of Defense (DOD)

The Department of Defense operates

380,000 buildings with a total fIoor space of

2.5 billion square feet. ” This includes

260,000 units of family housing in the United

States. It recognizes that energy costs are

becoming a major burden and a program is

now underway to install a variety of solarequipment designs on several typical DOD

building types. Some of the projects are

funded by DOE; some are funded internally.

The projects include:

–Shopping centers at Kirkland and Randolph Air Force Bases (heat and cool).

–Administration building at Fort Hood

(heat and cool).

— High-temperature water from concentrating collectors at Fort Carson, Colo.

—132 residential units on 16 Air Force,

Navy, and Army bases (heat).

–Three Army Reserve centers (heat and

cool).

— 50,000 square feet of classroom at Fort

Huachuca, Ariz.

–Air Force Academy housing (heat and

cool, funded by USAF).

– Refrigeration at the Navy regional medical center at Orlando, Fla.

According to a study conducted for DOD

by the BDM Corporation, solar photovoltaic

cells can compete with many generating devices now used to provide electricity to

remote sites, (Standard DOD techniques

were used to measure cost-effectiveness. )

The study estimated that DOD could purchase over $100 million of silicon solar cells

“ERDA-76-6, pp 71, 75.

annually without subsidy if the current price

of cells dropped by about 50 percent. 2 3

DOD is also testing the applicability of solar

power in several new DOD construction

projects and indications are that the results,

if promising, will be phased quickly into

other DOD construction and modernization

projects.

Veterans Administration (VA)

Several solar projects

in the VA’s 5-year plan:

have been proposed

● Retrofit of the San Diego VA Hospital

for solar heating and cooling.

● A solar-assisted heat pump for a new

VA hospital to be built in Palo Alto,

Cal if.

● Solar hot water systems for three new

hospitals under construction.

● 20 other projects were in the design

stage for FY 77; 40 more were i n the preliminary design stage for FY 78,

The VA’s 171 hospitals are built, operated,

and maintained by the VA itself, rather than

by the General Services Administration

(GSA), which is responsible for acquisition

and maintenance of the VA’s non hospital facilities (these are discussed under the GSA

program). Fuel expenditures for the 171 VA

hospitals amounted to $23.5 million in FY

75.

VA officials have informally indicated

that the agency’s hospital system could accommodate 120 solar installations, at a cost

of some $32 million. They estimate that retrofit would save $1.6 miIlion annualIy in fuel

costs and that this saving could be diverted

into a principal/interest debt repayment

fund for the solar equipment. ” To accomplish this, the VA’s 5-year Energy Plan would

have to be revised. But apparently no legislation nor additional funding would be required.

2 “’DOD Photovoltalc Energy Conversion Systems

Market Inventory and Analyses, ” Prepared for DOD

and FEA, spring 1977

24 Clark Granninger, VA, 1977
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 9 5

U.S. Postal Service (USPS)

An FEA-sponsored study found that USP S

“owns or operates approximately 75 million

square feet of floor space in 36,000 buildings. ” Of this floor space, approximately 80

percent is concentrated in 750 buildings. ”

The USPS has two solar demonstrations

underway: a new post office building under

construction in Ridley Park, Pa., and a retrofit project in Boulder, Colo A study is being

made of the possibility of designing solar

equipment for a standardized buiIding design which the USPS could use in many parts

of the country.

The USPS leases more than 80 percent of

its buildings from the private sector, and the

agency has the legislative authority and administrative flexibility to work any kind of

variation on utility payment responsibility

At present, however, it has no positive program for promoting the use of solar power in

its leasing program. The agency has not developed a comparative cost analysis system,

but USPS officials feel that regional USPS

personnel are professionally competent, as

welI as definitely inclined, to solicit solar as

part of its leasing program if encouraged to

do SO.

General Services Administration (GSA)

The General Services Administration has

jurisdiction over all Federal office space,

with the exception of post offices, DOD

facilities, VA hospitals, and certain other

specialized faciIities It has installed solar

equipment on only two Federal buildings —

one In Saginaw, Mich , the other in Manchester, N.H. Planned projects include:

. Heating and cooling faciIities i n a new

Border Patrol building at Marfa, Tex.

Ž Heating and cooling facilities at

Federal office buildings in Denver,

Colo , and Carbondale, III,

● Solar heating and cooling faciIities at a

Forest Service buiIding in Arizona

‘‘Sola r Energy Government flu I Id Ings Project,

hl I TR E (-orpor,it Ion, p 4

● RegionaI GSA adminstrators are soon

to make recommendations for solar energy projects for one or two GSA buildings in each region of the country,

GSA’s ability to install solar equipment is

limited by the fact that in recent years it has

often chosen to lease buildings rather than

to purchase them.

Health, Education, and Welfare (HEW)

The Department of Health, Education

and Welfare is charged with demonstrating

solar heating and cooling in Federal and

private hospitals and other health-care facilities as part of DOE commercial demonstration program. An interagency agreement

between DOE and HEW authorized HEW to

solicit proposals for such projects, it calls

for an “open” solicitation; that is, solar contractors are to be invited to make proposals

for heating and cooling demonstrations at

certain health care facilities Five or six projects are anticipated under the proposal, and

about $1 million in DOE funds is involved.

In addition, DOE has funded a $300,000

project for a solar installation at an Indian

health-care facility in New Mexico and a

project at a Public Health Service hospital,26

BUILDINGS OPERATED FULLY, OR IN PART,

UNDER REGULATIONS ESTABLISHED BY

THE FEDERAL GOVERNMENT

The Federal Government, in addition to

the buildings it owns or leases, supervises

the operation of many buildlngs that receive

Federal loans or operating subsidies The

Government could use Its leverage to encourage the use of solar-energy equipment

on such projects. In the case of buiIdings

which receive operating subsidles partialIy

attributable to energy costs, the Government might directly benefit from diverting

annual subsidy funds to programs designed

to capitalize solar devices.

The largest number of federalIy sponsored residential units have been con-

“Carl Conner, ERDA, priv.ite c omrnunl( .it Ion, 1977
96 ● Solar Technology to Today‘s Energy Needs

structed under public housing programs.

Over 1 million units of low-cost housing

have been constructed with federally subsidized municipal bonds since 1937. Projects

covered under Section 8 of the Housing Act

aIso receive annual payments to ensure that

tenants are charged no more than 15 to 25

percent of their annual income for rent,

Unfortunately, current accounting procedures make it difficuIt to determine the

fraction of annual subsidies attributable to

energy costs. HUD officials estimate that

energy costs currently account for 20 to 30

percent of the subsidy payments.

Public Housing

The Public Housing Program has funds for

modernizing existing structures (the approximately $20 mill ion available in FY 77 was

capitalized by local developers into about

$200 million in project funding). Energy conservation is considered a major objective of

recent modernization investments. However, HUD has no program-wide conservation goals. There are no real incentives for

local housing officials to invest in conservation equipment, largely for the following

reasons:

–There is a general feeling that the Federal Government wiII have to continue

to subsidize energy costs, and local officials therefore apply all availabl e

funds to other modernization projects.

–There is much less glamour in retrofitting older establishments with conservation equipment than in overseeing

innovative new projects. The effectiveness of area personnel tends to be

judged on the basis of their performance on newer projects.

Until late 1974, HUD’s legal staff had

ruled that operating subsidies for public

housing could not be used to capitalize investments in energy-conservation equipment. A more recent ruling changed that

opinion, and there are now judged to be no

legal barriers to using operating funds for

solar and other energy equipment. However,

there has been Iittle attempt to use operating funds for solar equipment, since HUD

officials are skeptical that solar devices

could be economically attractive on their

projects without additional Federal subsidies.

Acquired Housing

In addition to public housing, the Federal

Government acquires a substantial number

of residential units because of foreclosures

on VA, FHA, and FmHA loans (HUD currently owns approximately 90,000 such units).

The current policy is simply to dispose of

this property as rapidly as possible without

making modifications to the structures. It

might be desirable, however, to require that

the Federal Government provide certain of

these houses with energy-conserving equipment before they are resold.

ISSUE 4

Could any existing Federal grant program be

used to subsidize the purchase of solar- energy equipment?

Yes; many of them could, Some directgrant programs already have energy conservation as an explicit objective; others,

though initially designed for other purposes,

couId be used to administer funds for solar

insta I I at ions,

Taken together, funding for such programs totaled over a billion dollars in FY 77

and thus could be used to provide substantial subsidies for solar equipment—even if

only a small fraction of the funds could be

justified for this purpose. However, it will be

difficult to divert funds from many existing

programs because they are already oversubscribed for their primary purposes; in

these cases, solar equipment would have to

be paid for through additional funding. To

have solar grant money administered

through existing programs would have the

advantage of avoiding the addition of still

another separate program to what is already

a bewiIdering array.

If an attempt were to be made to coordinate these diverse and frequently overlap-
Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 9 7

ping programs in the interests of accelerating the commercialization of solar energy,

it would probably be desirable to use the

services of the Federal Regional Councils in

each of the 10 Federal regions nationwide.

Councils are headquartered in Atlanta, Boston, Chicago, Dallas, Denver, Kansas City,

New York, Philadelphia, San Francisco, and

Seattle These councils can use personnel

from several different agencies to coordinate programs across jurisdictional lines

and which receive funding from several different sources.

FEDERAL GRANT PROGRAMS

It will not be possible to summarize all

Federal grant programs which could be used

to subsidize solar energy systems. A few of

the programs which seem most immediately

relevant are:

Programs Administered by HUD

Community Development Block Grants are

provided under the Housing and Community

Development Act for a variety of urban renewal and community improvement activities which may include the rehabilitation of

housing. About $250 million was spent during FY 76 to secure loans totaIing about $500

miIIion Energy conservation was not a major priority of these programs since most of

the funds were needed simply to make

buildings habitable.

Housing Rehabilitation Programs are funded

under Section 312 of the same Act. Their

purpose is to rehabilitate housing and to ensure that housing meets the requirements of

local building codes. Use of these funds for

conservation is improbable because the program’s success tends to be measured by the

number of units completed. Solar installations would reduce this number.

Homeowner Grants are provided by Section 302 of the Housing and Community Development Act to assist persons needing

funds for housing repairs.

Homeowners Incentive Demonstration Programs, authorized under the FEA extension

act (Title IV), are designed to evaluate the

effectiveness of incentives for encouraging

homeowners to install energy-conservation

or solar energy devices, Two hundred milIion dollars were authorized for the program

in FY 77.

Housing Finance Interest Subsidies are provided under the 1974 Housing and Community Development Act. This Act allows HUD

to make grants to State housing finance

agencies that use the money to cover interest payments on bonds sold for rehabilitating housing. Buildings must be examined

by HUD before such grants are made. They

must meet HUD’s minimum property standards. (See Issue 2 for a discussion of the impact of these HUD standards.)

Programs Administered by the Department

of Energy

The Energy Conservation and Production Act

(P. L. 94-385) established a 3-year program in

which $200 m i I I ion would be given to people

with low incomes for the purpose of insulating and “weatherizing” their residences.

The funds are to be administered at the

local level by community action agencies

Standards for allowable improvements will

be established by the National Bureau of

Standards.

Programs Administered by the Department of Health,

Education, and We/fare

The Administration on Aging oversees a program which gives emergency relief to elderly

persons finding themselves unable to meet

rising fuel bilIs. Grants also are made to

State agencies which provide direct assistance in insulating and weatherizing residences .

27 The program is very modest; its

budget is approximately $1.5 million.

The Social Services Administration provides

up to $500 for winterization to families qualifying for Aid to Families with Dependent

Children. ” The program requires the recipients to match the amount of the Federal

grant

‘701der Americans Act, Title I I I

‘“Socla! SecurltY Act, SectIon 403
98 ● Solar Technology to Today’s Energy Needs

Programs Administered by the U.S.

Department of Agriculture

The Farmers Home Administration may

make loans or grants in amounts up to

$5,000 to low-income rural residents for the

purpose of improving their homes to meet

local code standards. z

’ The funds can also

be used to purchase insulation. Its applicabiIity to solar equipment is uncertain.

Programs Administered by the U.S. Department

of Commerce

The Economic Development Administration

is authorized by both the Public Works and

Economic Development Act of 1965 and by

the Public Works and Capital Development

and Investment Act to make grants to communities with the central objective of stimulating employment in regions with severe

unemployment problems. Annual expenditures are typically in the order of $200

milIion, although a special “one-shot” infusion of $2 billion was granted in 1976 because of severe unemployment problems.

It may be easier to use this program for

solar and conservation investments than any

other Federal grant program. This is because

money used for these purposes would not

have to compete with other, critical uses of

the Federal grant funds (e. g., housing rehabilitation). The object of the program is to

stimulate employment and, as shown elsewhere in this paper, solar energy is a laborintensive industry which requires skills in

job areas currently suffering serious unemployment. Funds from the CD I program,

however, are typically used for “public

works” projects which have high visibility.

FEDERAL INFORMATION PROGRAMS

In addition to the major grant programs

described above, a series of activities which

provide grants and/or technical services exist within the various Federal agencies.

These include such things as the Extension

Service of the U.S. Department of Agricul-

‘

9 Housing Act of 1949, Sect Ion 504

ture, the Product Dissemination Program of

HUD, the Comprehensive Employment and

Training Act administered by the Department of Labor, the Community Services Administration, and Action. Some of these programs are bringing energy conservation Into

their activities through various means.

These include grants for weatherization,

providing labor for performing this weatherization, and information services on reducing energy costs to homeowners.

These programs appear to have the flexibility to incorporate solar energy in their activities. As such, their contact with a large

portion of the American population could

serve to accelerate the penetration of solar

energy. A similar course is being proposed

with regard to the Energy Extension Service

now being developed by DOE.

ISSUE 5

When private companies are subsidized with

Federal funds to develop equipment for the

commercial market, how can a balance be

struck between the company’s need to retain

a useful proprietary interest in the technologies developed and the Nation’s right to

have complete disclosure of the results of

federally sponsored research?

There is no easy answer to this question.

But it raises what is likely to be a central

problem for all federally sponsored efforts

to develop small, commercially viable energy technology.

On the one hand, the public has a clear interest in ensuring the widest possible dissemination of research and development work

conducted under Federal auspices. This is

particularly important with onsite solar

equipment because many of the manufacturers are small, having neither large research staffs nor easy access to information

about a rapidly changing technology.

On the other hand, a company which is

not permitted to retain any proprietary information concerning the equipment it de-
Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy ● 9 9

velops with Federal funds may conclude

that it has no commercial interest in the

development. Without patent protection

and without any advantage of advanced

design knowledge, the company may determine that it cannot risk manufacturing the

equipment. The company would undoubtedly enjoy some competitive advantage as a

result of its research, if only because of the

experience and ideas it obtained. The Federal grant would have placed the firm on the

edge of the “state-of-the-art” in at least one

area of technology— a position that would

leave the company in a uniquely favorable

position to make further progress with its

own funds. Most of the commercial technologies which have “spun off” from research

sponsored by the Department of Defense

and by NASA have resulted from such situations. Even in situations where the complete

results of research work were published, the

companies involved retained valuable experience in the practical difficulties associated with manufacturing and design which

might be difficult or impossible to publish.

(A machinist who d is covers that a driII works

best if you spit on it before making a critical

hole, for example, may hold the key to a

problem which would require another company months to resolve. )

At present, the Government does not have

much flexibility in adjusting its policies in

this area Only NASA is now able to grant exclusive Iicense protection to products developed with FederaI support. Several innovative approaches have been proposed, however, and DOE is funding the development

of a new heat-engine design in an experimental arrangement with the Sunstrand Corporation. In this program, the Government is

acting very much Iike a private source of

“venture capita l,” giving partial development funding and retaining a partial interest

in the resuIt

A major effort should be made to explore

alternative approaches to Federal support

for commercial products, and to determine

their utllitv and jiustice to the taxpayer.

ISSUE 6

Should the Federal Solar Program include a

major effort to encourage competitiveness in

solar energy and promote small solar business?

The relatively small investments associated with onsite solar energy devices have

made it possible for many smalI businesses

to enter the market. Indeed, much of the innovative work now being done in the area

has emerged from firms with very limited

assets. This unique feature of the onsite

solar energy field presents a difficult choice

for the policy maker. A program for supporting small, relatively simple technologies will

have many more firms to choose from than

a program for developing large energy technologies, which require large capital investments in individual projects. Supporting

some of the small solar energy firms offers

an opportunity to explore a rich variety of

concepts without a massive investment in

any one approach, as well as a better opportunity to foster competition in the energy market. Apart from any such pragmatic

advantages, promoting small business has

always been considered a desirable objective in and of itself; the small, independent

competitive firm is still a cherished ideal of

the American economic system.

On the other hand, small firms are likely

to have Iimited marketing experience, no nationwide representatives and contacts, and

limited research funds. Some may be inefficiently managed and others have Iimited experience with the difficulties associated

with taking a good engineering concept, developing a marketable product, constructing equipment for mass production of comparable products, and developing sales and

advertising policy. The policy options offered in this paper do not resolve this dilemma; they give encouragement to small enterprises but do not include requirements

which ensure that small enterprises get a

specified share of Federal funding.

The Small Business Administration (SBA)

has played a very limited role in promoting

smalI solar energy businesses, although it
700 ● Solar Technology to Today’s Energy Needs

has begun to investigate the field as the

result of congressional prodding. SBA will

participate in DOE’s program to finance

selected energy-related inventions.

A separate but related issue concerns Federal policy on restraint of trade. It is apparent that solar energy systems, particularly

onsite devices, will increase competition in

the energy supply industry. A substantial

fraction of the cost of smaller solar systems

(particularly and virtually the entire cost of

passive solar systems) results from onsite

construction work which would be performed by local building contractors. The

building industry is one of the most competitive industries in the country, The diversity of approaches, the fact that different

climates will call for different systems, and

the relatively small investments required to

manufacture many simple types of solar devices will almost certainly maintain the

competitive nature of the solar manufacturing industry. There will, of course, be items

which can only be produced economically

in very large quantities. Production of sit icon solar cells, for example, probably must

take place in facilities capable of producing

5 to 50 MWe annually if low cell costs are to

be achieved.

The Federal Trade Commission is monitoring the solar industry to insure that existing

oil companies and utilities do not dominate

the field to the point of restraint of competition in the area. Both utilities and major oil

companies are entering the solar industry. A

majority of the photovoltaic devices manufactured in the United States for example,

are produced in subsidiaries of major oil

companies. Both the Electric Power Research Institute and American Gas Association have sponsored projects in solar energy

and a number of utilities have undertaken

projects on their own. (For example, the

Southern California Gas Company has been

involved in a large-scale program for demonstrating solar hot water in California since

1973. ) The Pennsylvania Gas and Water

Company acts as a manufacturer’s representative for solar collectors, and Gasco Inc. of

Honolulu has a direct merchandise arm

which sells collectors as well as gas appliances.

30 The advantages and difficulties of

utility participation in ownership of onsite

solar energy equipment is discussed in some

detail in chapters V and VI. It will be extremely difficult for any organization to

monopolize the solar industry because of

the inherent diversity of approaches; there

will probably always be intense competition

between different designs. Probably the

most serious danger to competitiveness in

the solar industry is the Federal Government

itself. The potential for competition between different organizations and different

engineering concepts could be distorted if

Federal funding is unwisely allocated.

ISSUE 7

What sort of consumer protection is required

in solar energy products?

The central problem, not surprisingly, is

the novelty of the equipment. Homeowners,

builders, architects, and the financial industry share these fears:

1, Will the system work as advertised?

2. How long will it last?

3. Will operational costs be prohibitive?

4. Will a solar unit hurt the resale value

of property on which it is installed?

5. Will the technology change so rapidly

that the equipment now available will

soon be obsolete?

These anxieties are intensified because: (a)

there are no standard techniques for presenting performance data on the variety of

different systems for sale, and (b) many systems are offered by small organizations

without substantial assets or wide experience in manufacturing. Indeed, many of the

firms now producing solar collectors, for example, are Iikely to vanish during the next 10

years, leaving their customers with equip-

‘“j H Williams, “Solar Energy and the Gas Utility, ”

February 1977 (Dlstrlbuted by the American Gas

Association )
Ch. III Federal Policy for Promoting and Regu/ating Onsite So/ar Energy ● 101

ment no one else is qualified to repair. That

part of the problem will get even worse, because potential buyers will be faced with an

ever-widening array of equipment and advertising c Iaims.

To be sure, any new technology undergoes such growing pains. And in due course

certain manufacturers will establish reputations for high-quality products and for backing their systems with attractive maintenance contracts. Unfortunately, it could

take years for this to happen — and in the

meantime some unscrupulous dealers are

likely to enter the field.

Can the Government help to remove most

of these concerns? It will be extremely difficult the way things look now — the Government itself is uncertain about the best

technical approaches to support, and it

shouId not be dogmatic anyway. However,

standards have been established for the

equipment the Government buys, and this

could provide some guidance for prospective purchasers. A process for developing

standards for solar heating and solar hot

water equipment has been underway for

some time, and plans are being made to certify a national testing laboratory which can

assure that tests are properly administered.

Progress on both fronts, however, has been

frustratingly slow Great care is needed to

make sure that such standards do not inadvertently eliminate novel approaches.

At a minimum, it will be necessary to

develop mechanisms to ensure that standards are updated to take account systematically of advances in solar technology. It

will not be an easy matter to work out standards for another reason: each subtechnology will require its own set of standards,

which must be arranged in such a way that

they are applicable to a variety of buiIding

sites Some such work has already been

done The National Bureau of Standards has

developed interim standards for solar heating and hot-water systems, and NASA-Lewis

has developed preliminary standards for the

photoelectrlc systems which wiII be purchased for electric generation.

The Government could also help by requiring that all systems sold bear performance ratings conducted under procedures

prescribed by Federal law.

Another major problem has been the

shortage of building inspectors trained to

recognize mistakes made in installing solar

equipment. InstalIation costs often represent a significant fraction of the total cost of

a solar system, and a large fraction of the

problems encountered with solar equipment

is attributable to improper installation. Federal support of training programs for inspectors could provide useful assistance in this

area.

However, none of these approaches can

eliminate the basic fear which surrounds a

novel technology. The most powerful influence on the public’s reaction to onsite

equipment will be the behavior of the solar

industry itself. Because of its strong selfinterest in policing itself, the industry may

welI be the best source of advice for ways in

which the Government might

ing consumer confidence

ISSUE 8

assist in buildWhat are the objectives of the solar demonstration program, and what criteria should be

applied to the systems demonstrated?

There has been considerable confusion in

both areas. On the one hand, demonstration

projects are presumably not a part of a research program since the systems demonstrated are presumably commercialIy available. On the other hand, there is little point

i n demonstrating that commerciaI systems

work if a market for them already exists or i n

demonstrating that they are too expensive if

there is no market. The program could be

used to reduce costs only if the program purchased so many units of a given type [halt

manufacturers could justify installing massproduction equipment, This course seems

undesirable, however, since funds used for

this purpose could probably be better used

to support tax incentives and loan assistance.
102 . Solar Technology to Today’s Energy Needs

Passively heated and cooled buildings are

perhaps a unique case, however. A large

number of concepts are possible, and it is

frequently difficult to predict how designs

wilI work or how much they add to construction cost without field demonstrations. A

large number of demonstrations is needed

since it is necessary to carefuIIy tailor designs to each climate (perhaps to each microclimate). Another possible objective of

the program is to provide information about

the lifetime, reliability, operating costs, and

unexpected problems associated with installations operated by inexperienced owners.

While information in this area is needed, the

use of expensive demonstration programs to

gather it must be justified carefully. At a

minimum, the demonstration programs

should be integrated with an effort to obtain

data in these areas using laboratory testing

equipment. An effort should be made to

publish the results of instrumented analysis

of the demonstration units in many different

climatic regions as soon as possible and to

communicate this information to building

designers in the area.

Information gathered about the cost of

the units purchased in connection with the

demonstration program must be treated

with great caution and cost data prepared

with considerable care. It is important, for

example, to separate costs incurred in the

demonstration unit which would not have

been incurred if the device were built without Federal support (the cost of instrumentation, for example, must be separated from

other costs). Interpretation of cost data is

difficult since, if the demonstration program

is choosing its sites properly, the demonstration solar device will be among the first of

its kind in the region. It is to be expected

that installers charge more for installing the

demonstration units than they would charge

once such installations become routine.

Mistakes encountered in the first-of-a-kind

installation can be avoided as experience is

gained.

Perhaps the most useful function of the

demonstration program is simply one of

propaganda: bringing solar energy systems

to the attention of the local population and

providing an example of a real, functioning

unit which can be visited by interested

building contractors, potential investors,

and other interested parties,

THE EXISTING MARKETING PLAN

There is a great deal of confusion in the

current program about which technologies

should be demonstrated, when they should

be demonstrated, and the size of the applications which should be chosen for demonstrations. The lack of a coordinated plan

has resulted in the following:

1.

2.

3.

A consistent underemphasis on retrofit

applications when the retrofit market is

much larger than the market for new

construction.

Underemphasis on combining solar and

conservation demonstrations, Passive

solar buildings have received little attention as a result.

Lack of planning to extend demonstration into electric generation and cogeneration equipment and into industrial

and commercial markets.

A lack of a systematic approach to these

technologies has resulted in many a situation where systems intermediate between

residential and large utility applications

have been given much too little attention.

Part of this distortion, of course, is inherent

in the unevenness of congressional support

for different kinds of programs.

Commercial and industrial facilities and

multifamily residential units are attractive

initial markets for solar equipment for a

number of reasons:

1.

2

It should be easier to retrofit solar

equipment on commercial buildings

than on residential buildings since running pipes from collectors to the heating and cooling equipment would disrupt a proportionately smaller part of

the building.

The owners of commercial buildings

tend to be more sophisticated at anal-
Ch, /// Feclera/ Po/icy for Promoting and Regulating Onsite Solar Energy ● 103

yzing life-cycle costing than owners of

single family residences.

3. Systems on commercial buildings may

4

5.

have greater visibility than systems i n

residential neighborhoods, and businesses would frequently advertise their

use of solar energy.

Cooling technology and some heat engine technology which is not ready for

residential demonstrations is now available for commercial demonstration.

Single commercial systems would have

a much greater impact on fuel consumption than an individual residence,

and would be easier to manage with a

smalI staff than numerous installations

on different types of residences.

ISSUE 9

Which Federal agencies are conducting solar

research programs, and how well are these

programs coordinated?

Those agencies with major responsibilities

in solar energy are DOE (which has been given responsibiIity for al I solar research programs and is developing programs to accelerate the commercialization of solar technologies which are ready for market) and

HUD (which is managing the residential

heating and cooling demonstration programs). I n addition to these major activities,

however, there are solar programs in the Department of Health, Education, and Welfare, the National Science Foundation

(which retains a small solar-energy staff

even though the bulk of research has been

transferred to DOE), the National Oceanic

and Atmospheric Administration [which collects such climatic data as sunlight intensities and wind-speeds for use in the evaluation of solar technology), the Defense Department (which is going to install a variety

of solar devices on military property, including electric systems for remote facilities], NASA (which has great institutional interest in the development of an orbiting

solar photovoltaic system — and is reportedly investing heavily in designs for such

systems out of internal funds — as well as using solar celIs to power spacecraft), the Department of Agriculture (which is developing solar heating for barns and other farm

buildings, along with equipment for agricultural process heat, irrigation pumps, etc.),

and the National Bureau of Standards

(which is developing standards and testing

procedures for solar equipment following initial work by NASA). The Department of the

Interior and many other agencies have

smaller programs, most of them for the installation of a solar hot water or heating

system at one of the agency’s buiIdings.

Still other Federal agencies are in a position to implement regulations affecting

solar energy systems. For example, the Federal Energy Regulatory Commissin(FERC)

in DOE (formerly the Federal Power Commission) is helping to develop design requirements for solar electric commercialization projects. The Veterans Administration

is examining the feasibility of allowing VA

loans to be used for solar equipment and is

planning to use solar equipment at some of

its hospitals. The section of HUD charged

with administering FHA loans is examining

the possibility of changing minimum property standards to permit funding of solar

equipment. The Council on Environmental

Quality is conducting an independent study

of solar heating and cooling for single family houses, The list could be extended.

To some extent, of course, duplication between agencies in solar research and development produces healthy competition. It

can prevent the development of a monolithic approach to solar-technology research

which could lock out innovative concepts.

On the whole, officials interviewed agree

that duplication exists, But they argue that

most work is complementary and that it is

coordinated with administration-wide solar

policy. They contend that each agency

should carry out its unique responsibility in

this area. Some say that funding solar development through a number of agencies probably results in a larger total solar budget

because it is easier for each of two depart-
104 ● Solar Technology to Today’s Energy Needs

ments to get a $2-million solar project than

it is for one department to get a single $4-

mill ion project.

There are, however, areas where confusion in management could create difficulties:

— Plans to change FHA and VA loans are

proceeding without any clear guidance

from DOE, which has a clear mandate

to commercialize solar energy technology.

– In the meantime, HUD has proceeded

to fulfill its mandate in the demonstration of residential units and is developing technical expertise and management experience in demonstrating novel solar technologies

–There have been some misunderstandings between NOAA and DOE over

which agency’s funds should be used to

maintain installations for developing a

data base on insolation, wind speed,

and ocean temperatures.

— Total energy studies are proceeding in

HUD and the National Bureau of Standards, as well as in DOE Coordination

between these programs could be improved

— Research in advanced heat engine technology relevant to solar energy is being

funded by DOD, NBS, the Departmen t

of Transportation, and NASA, as well as

by DOE In some cases duplication has

occurred. Coordination could be improved,

– Heavy NASA support of orbiting photovoltaic systems, not well coordinated

with DOE, could greatly distort the

overalI photovoltaic development program.

ISSUE 10

Does the present Federal program for developing solar electric generating equipment

overemphasize large, central station approaches at the expense of smaller, onsite

approaches?

In spite of recent changes that have upgraded research on electric generating systems for nonutil ty appl cations, the bulk of

DOE’s solar electric research program is directed at technologies designed exclusively

for large, central generating facilities Thi s

strategy has several difficuIties:

1 .

2

3

There is no clear indication that large

solar electric plants are more efficient

or produce less costly energy than

smalIer, onsite faciIities

The large-scale projects being examined are very unlikely to make a contribution to commercial energy supplies before the 1990’s; smaller devices

may have greater potential for making

contributions in the near future

The very large solar electric system being contemplated will require simultaneous development of several novel

types of technologies (collectors, receivers, storage devices, etc. ) These

systems will be required to operate on a

large scale in the proposed multi-megawatt systems. It may be better to test

and evaluate components on a smaller

scale, or to develop components which

could be used on a variety of systems of

different sizes.

4, Concentration on large systems requires that difficult choices be made

between many competing approaches

before any of the alternatives have

been adequately tested. Funding smaller projects would permit greater numbers of concepts to be tested at much

lower risk.

DOE officials recognize that there are

numerous total energy concepts and proposals for generating electricity for specialized agricultural and industrial applications,

where available technology could be used in

an expanded demonstration program, But

they also note that additional funding would

require additional staffing, which remains as

the Office of Solar & Geothermal Energy

Program’s largest problem. The solar program does project a number of experimental

projects, which could include agricultural

process heat, small community applications, agricultural and industrial centers,
Ch. /// Federal Policy for Promoting and Regulating Onsite Solar Energy ● 105

and several other projects in thermal electric generation. At least one project of each

type of total energy could be built to research problems and demonstrate potential.

Programs to develop heat engines and storage apparatus compatible with onsite electric equipment also appear to be supported

at much lower levels than is warranted by

the equipment’s potential.

ISSUE 11

What kinds of research need increased emphasis in the Federal solar program?

COLLECTORS

Supporting the development of advanced

collector design presents special difficulties

since there are a large number of devices being developed independent of Federal funding and the number of possible designs is extremely large. The development of reliable,

inexpensive coIlectors is, however, probably

the single most important technical problem

faced by the solar community.

Federal support has concentrated in four

areas: 1 ) improving the design of flat-plate

colIectors used in connection with the heati ng and coollng demonstration program; 2)

developing heliostats for the central receiver demonstration projects; 3) developing

and testing materials for use in collectors

(e.g. , low-cost plastics for covers and receivers), and 4) developing a series of distributed

coIIector designs in connection with the total energy program While the last program

has been effectlve in testing a variety of collectors, an even greater variety must remain

withiout serious Federal support. For example, relatively Iittle attention has been paid

to the development of Inexpensive pond collector and simple, Iightweight two-axis concentrators for use with smalI heat engines

and photovoitaic devices designed for use in

high-intensity sunlight One major difficulty

with many federally sponsored designs has

been the temptation to “over-engineer” devices rather than to emphasize techniques

for simplicity, low material requirements,

and low cost.

HEAT ENGINES

An enormous range of technical possibilities for heat engines is relevant to solar applications. While heat engines currently

available can be used in near-term solar

energy designs, few of the engines have

been designed especially for solar applications — modifications of engines produced

for some other application will be used. Additionally, most near-term applications of

solar energy will utiIize smalIer heat engines

than those typically used in utility operations, and the technology for small heat

engines which can operate from an external

heat source is frequently not as advanced as

the technology used for large central powerplants, in many cases, the only small heat

engines available are based on European

designs.

The development of improved heat engines would unquestionably lower the cost

of solar energy for applications requiring a

high ratio of electrical to thermal energy

New devices which could make efficient use

of low-temperature solar heat sources could

reduce the complexity of solar colIectors required for power generation. More efficient

heat engines can reduce total system costs

by reducing the size of the collector field

needed to provide a given amount of electrical or mechanical energy since collector

costs tend to dominate overall system costs.

Development of a high-performance Stirling, Ericsson, or closed-cycle Brayton

device would open many attractive options

for solar electric generation. Development

of improved cogenerating systems would

improve the overalI utilization of the solar

energy received in applications where there

is a requirement for thermal energy,

Most federally supported work on advanced heat engines, however, is relevant

only for large central powerplants and the

funds available for engines designed for

solar, transportation, and industrial applica -

tions are very Iimited,

Background on Federal Programs

Most other work on advanced heat engines in DOE is being funded by the Office
106 ● Solar Technology to Today’s Energy Needs

of Conservation. Projects are funded in

three categories:

1. Heat engine research in the Division of

Transportation Energy Conservation.31

Development of new heat engines for automobiles and other road vehicles is being

coordinated with major U.S. automobile

manufacturers who apparently are unwilling

to fund development of advanced engines

without Federal prompting.

Three projects are of particular interest

for solar applications:

●

●

●

A program is underway to develop an

efficient Brayton-cycle (gas turbine) engine. In the past years, tests have accumulated the equivalent of over 150,000

road-miles on some designs. Work is

also underway to develop ceramic engine components capable of withstanding very high temperatures (2,500” F).

The government will purchase seven

GeneraI Motors Brayton engines during

FY 78 for $500,000. The engines will be

used for road tests.

The Government is also contributing to

the Ford/Philips program to develop a

Stirling engine for road vehicles. This

work will include continuing tests on

the current 170 hp design and development of a smalIer (80 to 100 hp) design.

Work next year will include completing

engine performance and emission tests

and improvements on the difficult

“heater” heat exchanger which has

plagued the Philips design. DOE is contributing about $1.6 million to this project in a cost-sharing program during FY

78.33

Development of an organic Rankine device to increase the efficiency of a

truck diesel engine is also being supported. This combined-cycle design

would replace the truck’s muffler with

a boiler for the organic fluid,

“ ERDA Budget Estimates (Amended FY 78), Book 1,

p 57

“lbld , p 96

‘

) Division of Transportation, Office of Conservation, DOE

2.

3.

About $12 million will be spent on new

heat engines during FY 78 by the “heat

utilization” section of the Office of Conservation. 34 Projects funded in this area

will include support for two high-temperature expanders which might be

used for combined cycles, support for

designs which will increase the pumping efficiency of engines .35 Research on

small devices will include the development of efficient steam turbine systems

in the 2 to 6 MW range and studies of

Stirling engine applications. The Stirling work will include studies of designs

suitable for solar applications as well as

designs compatible with total 500 to

2,000 horsepower energy systems in residences and industry. It is hoped that a

Stirling device for utility applications

could be produced commercially by

1982. 36 Work on Stirling engines is also

underway in DOE’s Office of Nuclear

Energy Programs, DOD, NASA, and the

National Bureau of Standards, but conservation and solar applications officials claim there is Iittle duplication. 37

Work is also being supported which will

examine engines for topping or bottoming cycles for utilities and for industrial

processes. Therm ionic devices for hightemperature topping is being supported

with the objective of actualIy operating

a device in a boiler by 1980.38 Three different designs for organic Rankine cycle devices are being supported for use

with medium-temperature waste heat

streams. Work on low-temperature systems is beginning, although its exact

structure seems somewhat vague.

Work on advanced heat engine designs is

also being supported by the Fossil and

Nuclear Energy Office of DOE. These de-

“ERDA Budget Estimates (Amended FY 78), p 80

“lbtd., p 82

“John Beldlng, Research and Technology Dlvislon,

Office of Conservation, DOE, private communication, 1977

‘

7 George Pezdlrtz, Off Ice of Conservation, private

communication, 1977

“ERDA Budget, p 86
Ch. /// Federal Policy for Promoting and Regulating Onsite Solar Energy Ž 107

signs are, almost without exception, applicable only to large central power applications. The fossil energy coal program has requested $25.5 million in FY 78 budget authority to develop advanced power systems

including combined cycle and Brayton cycle

devices. 39 The Nuclear Research and Applications Office of DOE is financing two

studies into Stirling engines, one totaling

almost $5 m i II ion to develop a Stirling isotope power system, contracted with General

Electric, and the other with Mechanical

Technologies, Inc., totaling more than $1.5

m i I I ion.

In addition, Nuclear Research and Applications is funding a $2-million-a-year study

by Garrett Air Research, Inc., of Phoenix to

develop a 1.3 kilowatt Brayton isotope

power system, as well as a similarly financed

study by Sunstrand Corp to develop an organic Rankine device, also for a 1.3 kilowatt

system. Both are due to be demonstrated

during 1978; Nuclear Research and Applications officials say the choice will then be

made between the two systems 40

PHOTOVOLTAICS

A well-designed photovoltaic program

must maintain a carefuI balance between

basic research, development improvements

to current manufacturing processes, and engineering work on practical system designs.

This is a difficult task since the field is

changing very rapidly It would be tempting

to delay major decisions in the area until

research work has sorted itself out, but it

should be possible to design a balanced program, supporting production and demonstration work in areas where prospects of

success seem particuIarly high whiIe continuing to give support to advanced concepts.

(At a minimum, there seems to be no point

in waiting for “research breakthrough” from

arty of these devices without supporting a

vigorous research program, )

There is room for a considerable amount

of research on the bas]c physics and chem-

‘

9 Fos511 E nerg}, E KDA ~u~get, P 45

‘“Robert Morrow, NRA, 1977

istry of photovoltaic devices. Serious work

in the area of developing materials for terrestrial solar celIs has been underway for

only about 5 years. Work on the crystallography, electrical, and optical properties of

silicon and other photovoltaic materials

could be extremely useful. The properties of

amorphous materials, which may have applications in photovoltaic devices, are still

largely unknown,

The variety of cell designs which have

been proposed for use in inexpensive flat arrays and in various types of concentrators is

discussed in detail in chapter X. Many advanced cell concepts are receiving minimal

Federal support.

Finally, a number of fundamental questions about the most effective use of photovoltaic equipment must be resolved. Detailed system design work will need to be

done on the following topics:

– Mounting and support (e. g., should lowcost celIs be used as a buiIding material ?).

–What kind of cell cooling should be

used ?

— How should the systems best be integrated into existing utility systems?

Should onsite or utility storage be used?

Should the system sell as well as buy

from an electric utility? Should an electric backup or onsite generator burning

fossil fuel be used when solar resources

are not avaiIable?

— How often should the devices be

cleaned ?

In the near term, it will be necessary to

design practical and reliable systems

for remote (often unattended) installations

STORAGE

The present DOE storage program IS domi nated by two objectives 1 ) develop I ng very

large storage systems capable of operating

i n electric u t I I i ties to ‘‘level” the loads met

by these utilities, and 2) the development of
108 ● So/ar Technology to Today’s Energy Needs

batteries for electric vehicles. Relatively

little work is being conducted expressly for

solar energy or for other onsite applications.

There is, for example, presently no technique for adequately evaluating the complex issues of load management, transmission, and economies of scale for an integrated energy system.

Simple systems for storing relatively lowtemperature thermal energy or chilled liqu ids in tanks, ponds, and aquifers — systems

which appear very promising in the analysis

conducted in this report — have received

relatively Iittle support or interest, An enormous amount of fundamental work in thermochemical storage systems remains to be

done, and a number of known reactions

have been characterized well enough to

merit accelerated engineering development

work, A number of simple systems for storing high-temperature energy in latent and

specific sensible and latent heat have never

received serious engineering design work. A

number of other advanced storage systems

(batteries, flywheels, and other devices)

couId also profit from greater attention.

Background on Federal Storage Programs

In the Division of Energy Storage Systems

of DOE, a program has been developed to

investigate a variety of thermal and chemical storage techniques. The m a i n objective

of these studies is to examine the feasibility

of storing heat or electricity in order to level

the loads of major utilities, although t h e

technologies developed will probably be

directly applicable to solar energy systetms

for which the storage requirements are similar. Research will be required, however, to

adapt such systems to solar applications.

Adaptation may be particularly difficult for

onsite systems which may have storage requirements many times smaller than the

smallest utiIity units tested under this program.

The storage program has an objective of

developing batteries with an overall efficiency of 75 percent, and a 10-year installed

lifetime (approximately 2,500 deep cycles),

at a cost of less than $30 per kWh of storage

capacity. This program is also supporting

research to develop inexpensive and efficient inverters for turning d.c. into a.c.

power; such systems are needed to make efficient use of batteries. Again, the primary

objective is the development of technology

for utility load leveling.

The electric vehicle storage program in

the Division of Energy Storage Systems is

examining a number of advanced batteries

which have low cost and low weight, and

which last 4 years. I n normal use the technology which DOE apparently feels has

most promise in this area is the Iithium/iron

sulfide battery, although different pairs of

reactors are being sought. Three firms fabricated such devices and delivered them to

DOE for testing in FY 7841 DOE’s utility battery program has the objective of producing

batteries capable of 75-percent efficiency

and 10-year Iifetimes in normal utility applications. Work on a large battery storage

test facility in New Jersey financed jointly

with the EIectric Power Research Institute

began in FY 77.42 The first batteries in this

realistic utility environment will be lead

acid batteries, but advanced batteries (probably zinc-chloride and sodium-sulphur batteries) will be tested in the next phase.

Lithium/iron sulfide devices may be installed by FY 81. DOE is officialIy optimistic

about the potential of these batteries and

believes that the goal of $30 per kWh of

capacity can be achieved.

Solar technology could also make profitable use of the variety of advanced energy

storage techniques being considered in the

Division of Energy Storage Systems. Hydrogen production and storage, underground

pumped hydroelectric storage, underground

compressed air storage, flywheels, and magnetic storage are all receiving at least some

attention in the current program. Many of

the secondary objectives of the energy storage program are also directly relevant to

solar technologies. For example, the pro4’ERDA Conservation Budget FY 78, revised p 22ff

“lbld
Ch. /// Fecfera/ Po/icy for Promoting and Regulating Onsite Solar Energy ● 109

gram to increase the efficiency of building

space-conditioning and the use of industrial

process heat through the judicious use of

thermal storage techniques has clear relevance to solar programs. Major field tests of

seasonal and load-leveling storage for buildings are being conducted with the objective

of improving the efficiency of conventional

heating and cooling systems by 10 percent,

and a major portion of the FY 77 funds for

thermal storage were used to start work on

seasonal storage and structural materials

with thermal storage properties for use in

buildings.

ISSUE 12

Should funding levels in DOE programs correlate to relative estimated contribution of

different technologies?

Tables I II-4 and I II-5 compare the percentage of DOE solar funding given to three

major solar energy applications with projections of the potential energy contribution of

each solar application in the year 2000. No

clear correlation is apparent. EIectricity generated by solar systems, for example, is expected to represent only about 34 percent of

the total contribution of solar equipment in

the year 2000 but is receiving 64 percent of

the funding, while industrial process heat is

expected to provide 52 percent of the energy generated by solar equipment while receiving only 4 percent of the funding.

DOE has given solar electric power “highest priority” in its planning because of its

potential as an “inexhaustible resource”

and, it is claimed, it will “be given priority

comparable to fusion and the breeder reactors.” 43 Solar thermal systems, however, are

relegated to a lower priority and characterized only as technologies which should be

pursued only to “provide an energy ‘margin’

in the event of an R&D failure in other

areas.” 44

4

‘E RDA-76

‘“l bid

Table ill-4.—Authorizing Appropriations for the Energy Research and Development Administration,

U.S. House of Representatives, 95th Congress {1st Session], Conference Report No. 95-671

—. . ——.

Demand sector

cultural proSOURCES H qh demand esf I Imat{ from ERDA 48 Vol 1 UB 11

Low demand estimate based orI a 1000 demand srenarl{~ constrw-ted by !he Inst Itute for Energy Analysls

FY78 Budqet Au!hor!ty from U S House of Representat,+cs Con ferr, n ‘e Report Au Iborlr ng Appropraiiuns f ,r the Energy Research and

Deve 10 D m~n I Ad m I n [strat on October 6 1977 p 61 E R DA solar;}r[ ~C u 1 (n g ua Is t, I Ier le(~ and re ported n S Ild r En< rq y A IJ: I I,- at c ns — A

Com parat!. e A nalys(s to t h e year 2020 Summary Rep)d Draft J u Iy 1977 prepared by the M I t re Corporation Me !rek D IV IS !on
110 ● Solar Technology to Today’s Energy Needs

Table 111.5.—Authorizing Appropriations for the Energy Research and

Development Administration, U.S. House of Representatives, 95th Congress

[1st session], Conference Report No. 95-671

Heating and cooling of buildings . . . . . .

Agricultural and industrial process ... , .

Solar electric . . . . . . . . . . . . . . . . . . . . . . .

Heating & coolng . . . . . . . . . . . . . . . . . .

Agricultural and industrial process . . . . .

Solar thermal . . . . . . . . . . . . . . . . . . . . . . .

Photovoltaics. . . . . . . . . . . . . . . . . . . . . .

Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ocean thermal . . . . . . . . . . . . . . . . . . . .

Satellite power systems . . . . . . . . . . . . .

Operating Capital

expenses equipment

Plant Total

94.4 2.0

10.3 0

210.7 5.4

TOTAL SOLAR ELECTRIC . . . . . . . . .

Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . .

It is difficult to evaluate those arguments

since a comprehensive plan for integrating

Federal and industrial investments in solar

research has not been developed, and there

is no clear technique for determining when

the time has arrived for Federal research

support to be phased out and other types of

nontechnical support initiated. I n addition,

there has never been a comprehensive examination by DOE of either the economies and

diseconomies of scale in solar technology or

the relative merits of direct-thermal, electric, and combined electric and thermal

operations.

ISSUE 13

The Solar Energy Research Institute, in its

present operating relationship with DOE,

may not be sufficiently independent of DOE

to effectively meet its responsibilities in

reaching the objectives set forth by Congress in the Solar Energy Research, Development, and Demonstration Act of 1974.

In the Solar Energy Research, Development, and Demonstration Act of 1974, Congress found that “it is in the Nation’s interest

94.4 2.0

10.3 0

61.1 3.0

76.2 0.3

35.3 1.4

2.8 0

2.8 0

210.7 5.4

20.5 0.5

41

0

0

41.0

0

0

0

0

41

0

96.4

10,3

216.1

96.4

10.3

105.1

76,5

36.5

2,8

2.8

256.9

21.0

to expedite the long-term development of

solar energy, ” and “. that the Nation

undertake an intensive research, development, and demonstration program” in solar

energy, As a consequence, Congress declared that it was the policy of the Federal

Government to “pursue a vigorous and viable program of research of solar energy .; and provide for the development and

demonstration of practicable means to employ solar energy on a commercial scale. ”

To enable the Nation to fulfill this policy,

Congress established, in the same Act, the

Solar Energy Research Institute (SE RI) to

“perform such research, development, and

related functions” as determined by the

DOE, “or to be otherwise in furtherance of

the purpose and objectives of this Act. ” In

other words, it was the intent of Congress

that SE RI, while providing support to DOE,

should also be able to provide independent

direction and assessment of the Nation’s effort to develop solar energy. This was reiterated at oversight hearings held a year

after the passage of the Act. There it was

stated that Congress intended that SERI be

“highly visible” and be an institute symbolic

of the “national wiII and the national effort”
Ch. Ill Federa/ Policy for Promoting and Regulating Onsite Solar Energy Ž 111

toward solar energy, It is clear, therefore,

that the Congress did not want SERI to be

completely dominated by any other organization responsible for portions of the Federal

solar energy program.

Since the startup of SERI nearly 1 year

ago, however, it appears this intent is not being met. I n particular, the present method of

funding SERI is to enact a “tax” on other

programs under the Assistant Secretary of

Research and Technology. No separate line

item for SE RI appears in the budget; this

severely Iimits the abiIity of Congress to

directly evaluate the effectiveness of SERI

through the budget process. Furthermore, it

is not clear whether SERI can report directly

to Congress without DOE approval and

c Iearance.

SERI must maintain an ability to fairly

assess and, if necessary, criticize the direction DOE takes on developing solar energy,

if it is to fulfill the original intent of the Act.

A clear congressional reaffirmation of

SERI’s responsibility and mission and separate funding status within the DOE budget,

wouId contribute significantly to SERI's independence In addition, it may be desirable

to establish a more direct Iink between Congress and SERI to emphasize the intent of

Congress that SERI be a “visible” and “symbolic” institute of the Federal policy toward

development of solar energy and not simply

another group to carry out current DOE

polIcy

ISSUE 14

Staffing Limitations

A per~lstent shortage of protesslonal staff

h.~s be(~n .I major con~triiint on DOE’s ability

to adequately manage the rapidly changing

and growing solar program. The FY 76 solar

budget, for example, was $116 million, but

only 46 staff professional positions were

allowed. This amounted to just over $2.5

mill ion per professional. The problem became even worse in FY 77, with a budget of

$290 million to be spent by 54 professionals — amounting to nearly $5.5 million per

professional. The management of such large

amounts of funding is particularly difficult

in solar energy technologies, where the

typical contract is much smaller than the

average contract grant made by other sections of DOE.

The staffing shortage can create two

types of problems:

1 .

2.

It makes it difficult for DOE to react to

a large number of innovative ideas and

increases the temptation to spen d

funds in a small number of major and

predictable projects rather than in a

larger number of smaller projects some

of which may have a higher risk.

It necessitates transfer of the detailed

management responsibility to organizations outside the DOE’s Solar Energy

Division.

The problem associated with short staffing have been aggravated by demands

placed on staff by the continuing, extensive

public and congressional interest in solar energy which is flooding DOE with inquiries,

Much of this difficulty has been relieved

under a grant to Franklin Institute, whic h

has set up a toll-free number (800-523-2929)

to answer inquiries about solar energy.
Chapter IV

ONSITE ELECTRIC-POWER

GENERATION
Chapter IV.—ONSITE ELECTRIC-POWER GENERATION

Page

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

Capital Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

Generating Plants . . . . . . . . . . . . . . . . . . . . . . 118

Storage Devices. . ......................119

SolarCollectors . . . . . . . .................123

OtherAspectsofCapitalCost Comparisons 124

Waste-HeatUtilization . . . . . . . . . . . . . . . . . . . . 125

OperatingCosts ...... ● ..*..... ...*.**.. 129

Reliability .*.*.... . . . . . . . . . ..... . . . . . 129

Siting Problems. . . . . . . . . . . . . . . . . . . . . . . . . .133

MiscellaneousOperatingProbiems ... ......134

LIST OF TABLES

TableNo. Page

1. 1985 Generation Costs as a Function of

PlantSize. . . . . . . . . ....................118

2. lmpacts of Energy Storage on Electric

PowerSystems. . . . . . .................,123

3. Load Factors forTypical Buildings . ......126

4. OperatingCosts of VariousSystems .. ....130

Table No. Page

5. Engine Requirements for Systems Designed

to Provide ReliabilityEquivalent to Utility

Power Reliability. . .....................131

6. Reliability of Onsite Equipment . .........132

LIST OF FIGURES

Figure No. Page

1. Trend in Self-Generation . ...............115

2. Data From Steamplant Surveys, 1965-77...120

3. Steamplant Survey Results Showing

Average Unavailability Versus Size for

Plants Completed During the Survey

Period. . . . . . . . . . . . . . . . . . . . . . ..........122

4. Historic and Projected Load Factors

of Utility Generating Facilities . ..........125

5. Components of a District Heating

System in Sweden . . . . . . . . . . . . . . . . . . . . . 128

6. Annual Operating Costs Versus Equivalent

Full-Power Hours of Operation for

Baseload Plants . . . . . . . . . . . . . . . . . . . . . . . 131

7. Space Requirements of Typical Combined-Cycle Plants. . . . . . . . . . . . . . . . . . . . . 135
Chapter IV

Onsite Electric-Power Generation

BACKGROUND

While most electricity generated in the United States originates in large,

centralized facilities owned and operated by electric utilities, the number of

onsite generating plants has declined steadily and the average size of utility

generating plants has steadily increased. Figure IV-1 shows, for example, that

onsite generating equipment represented nearly 30 percent of all U.S.

generating capacity in 1920 but only 4.2 percent in 1973. ’ The percentage of

electricity generated in plants with a capacity greater than 500 MW, however,

increased from 40 percent in 1965 to 56 percent in 1974.2

Since many of the benefits and problems of onsite solar equipment are

shared by on site generating devices of all types, an examination of the potential market for the solar equipment must determine whether any of the

economic and institutional circumstances which produced the trend toward

centralization might change during the next two decades. There are two

reasons for undertaking an examination of this rather fundamental issue. The

most obvious is that the ways in which energy is produced and consumed

around the world will need to change dramatically during the next three

decades, if only because reserves of inexpensive oil and natural gas will

vanish during this period. These changes will require a reevaluation of alI conventional assumptions about energy. Secondly, the prospects for onsite

generation may be improved by newly developed technologies—especially

solar energy equipment. The solar resource is inherently distributed and

economies of scale are often difficult to identify.

There are a number of explanations for

the trend toward centralization:

●

●

●

●

Larger equipment tended to be less expensive per unit of installed capacity

Larger plants tended to be more efficient in their use of fuel and had lower

maintenance costs per unit output,

since a relatively small number of

trained operators could reliably maintain large generating plants.

Larger plants could be installed in remote locations, simplifying siting problems and ensuring that pollutants

would be released at a distance from

populated areas.

In recent years, a major advantage of

large plants was their ability to use coal

instead of oil and gas as a fuel. The

delivery of coal to a large plant, using a

dedicated rail facility, could significantly reduce the effective cost of coal

fuel.

115
116 ● Solar Technology to Today’s Energy Needs

●

●

●

●

●

●

●

●

Onsite facilities were frequently unable

to compete with “promotional” rates

charged during the periods when utilities were enjoying declining marginal

costs. Under those circumstances, all

utiIity customers benefited from increased sales, since average rates

declined as utility sales expanded.

Many companies were reluctant to invest in onsite equipment because they

were unable to finance a large fraction

of the equipment with their own equity,

They were forced to turn instead to

debt financing, which had the effect of

increasing company vulnerability during periods of economic hardship, This

meant that greater returns were expected of onsite generating equipment

than were expected of investments in

product-oriented areas.

There was a fear that a failure of onsite

equipment could have disastrous effects on the operation of a business,

and a feeling that the headaches of

electricity production should be left to

the utilities, whose primary business

was energy.

Electric utilities have frequently opposed the installation of onsite generating facilities by industry and have

often been reluctant to own such equipment themselves.

Many onsite facilities have been poorly

designed and have received inexpert

maintenance, and reports of failures

have frightened prospective investors.

Onsite generating equipment has tended to be of somewhat archaic design.

Federal and industrial research has concentrated almost exclusively on the

development of improvements in large

centralized equipment rather than in

systems optimally designed for onsite

generation.

Onsite equipment in some installations

has created problems of noise and local

pollution, and some owners have encountered difficulties in expanding generating faciIities.

One of the major objectives of this study

is to determine whether there are or will be

circumstances under which the advantages

of onsite energy equipment, particularly

solar energy equipment, can outweigh this

rather impressive set of traditional reasons

for avoiding onsite equipment. It is interesting to observe that many nations

which have experienced higher fossil fuel

prices than the United States make far

greater use of onsite electric power. For example, 29 percent of the electricity generated in West Germany is produce

industrial plants. 3

Onsite equipment can offer a

advantages:

●

●

Location of equipment “onsite"

d by onsite

number of

greatl y

increases the design opportunities and

makes it easier to match energy equipment to specific onsite energy demands. In particular, it should make it

easier to use the thermal output of

solar collectors and the heat rejected

by electric generating systems which is

typically discarded (often at some environmental cost) and wasted by central generating facilities. There is a considerable amount of overlap between

equipment being developed for energy

conservation and onsite generating devices, and onsite designs are usually

most successful when integrated into a

coherent plan encompassing both energy demand and supply.

The basic solar energy resource is available onsite whether it is captured or

not. Integrating the equipment into the

wails or roof of a building or into the

landscape around a building can reduce the land which must be uniquely

assigned to solar energy. Onsite generation of energy can reduce the cost of

transporting energy and reduce the

losses and environmental problems

3 R Sukhula, et al (Thermo-Electron Corp ), A

Study of Inplant Electric Power Generation in the

Chemical, Petroleum Refining, and Paper and Pulp industries, june 1976, pp 1-4
Ch. IV Onsite E/ectric-Power Generation ● 117

associated with transmission. (The extent of these savings can be difficult to

compute, and this topic is treated with

greater care in chapter V.)

Ž Onsite equipment can reduce investment risks, because it can be constructed rapidly and additional units

can be installed quickly to meet unexpected changes in demand.

● Onsite equipment can be made as efficient as centralized equipment, even if

no attempt is made to use thermal

energy exhausted by generating devices, If this heat is applied usefully,

overall efficiencies as high as 85 percent are possible.

● High-efficiency energy use, possible

with combined electric and thermal

generation, can result in a reduction of

polluting emissions produced by onsite

devices burning conventional fuels.

Ž Onsite equipment can be manufactured, installed, and maintained without major changes in the way energyrelated equipment has been handled in

the past. It would not require novel approaches to financing, new types of

businesses, major new categories of

labor skills, or major participation by

the Government.

In addition, there may be social, strategic,

or political reasons for trying to reverse the

trend toward increasing centralization of

energy production in the United States

which have no direct connection with the

economic merits of the case. Some of these

issues are discussed in chapter VI 1.

In assessing the relative merits of large

and small equipment, it is necessary to

judge both as a part of an integrated energy

system. Reviewing the performance of units

operating in isolation can be very misleading.

In particular, it is necessary to distinguish

between the advantages enjoyed by large

energy systems, which result from economies of scale in individual devices, from

the advantages resulting from the fact that

the large systems meet a demand relatively

free of the sharp demand peaks which characterize individual energy customers. The

smooth demand results from combining

many customers into a single diverse load,

and this advantage could be enjoyed by

small generating centers able to buy and selI

energy from a large energy transmission and

distribution system.

Since the primary objective of improving

an energy system is to reduce the net price

paid for energy by all consumers, it is

necessary to try to show how each component will affect the overall price of meeting real fluctuating demands for energy

throughout the year. This clearly is not a

simple undertaking, particularly since so

many changes can be expected in the way

energy will be generated and used during

the next few decades. Many new technologies wilI undoubtedly emerge in generating, storage equipment of all sizes, and in

the technology of energy transport.

Energy can be transmitted in electrical,

thermal, or chemical form, for example, and

stored as mechanical, thermal, or chemical

potential energy Energy can be generated

at a central facility and sent for storage in

onsite units (it is common in Europe, for example, to store electricity which wilI be used

for space heating in the form of heated

bricks), and energy generated locally could

be sent to a central facility for storage

optimizing the combination of onslte and

central energy devices will be difficult b e -

cause of the many variables and uncertainties, but the outcome of this analysis can

profoundly affect perceptions about the

relative value of different types of equipment and it can affect the designs chosen

for onsite systems These issues are treated

in more detaiI in the next chapter
118 ● Solar Technology to Today’s Energy Needs

CAPITAL COSTS

The only satisfactory technique for comparing the cost of onsite and centralized

power generation is to undertake the detailed comparison of life-cycle costs of integrated systems which is undertaken in

detail in volume 11. It is interesting to notice,

however, that there frequently is no clear

correlation between the size and the unit

cost of generating and storage components.

Comparisons between different sizes of

equipment based on the same basic design

can be misleading; it is important to compare the costs and performance of devices

selected to perform optimally at the size

range selected.

GENERATING PLANTS

Table IV-I indicates that the initial costs

of onsite generating equipment may actually be less than the cost of larger pIants per

unit of generating capacity.

Table IV-1 .—1985 Generation Costs as a Function of Plant Size (1975 dollars)
Ch. IV Onsite Electric-Power Generation ● 119

Review of Electrical Wor/d’s Steam Station Cost Surveys for the past 22 years’

showed that, from 1965 to 1975, there was

no significant decline in capital costs of

steam plants of all types as their size increased. Figure IV-2 shows costs per unit of

generating capacity as a function of plant

size for steam plants completed from 1965

to 1977 Only the 1977 survey gives any inclination of economies of scale, and the

limited number of plants in that summary

compared to previous surveys makes it very

difficult to conclude that economies O f

scale may again be valid.

Another trend determined in this review is

that unavailability frequently increases as

size increases, resulting in higher effective

capital costs (figure IV-3). It should be noted

that the stations reviewed in these surveys

are new, and the availability problems may

result in part from breaking in the new

plants

While small units manufactured in small

numbers may be substantially more expensive per unit output than large systems, the

cost of small systems can be substantially

reduced using mass production techniques

unsuitable for larger devices. Moreover, investments in large generating faciIities are

so substantial that very conservative design

practices must be used. SmalIer systems permit greater experimentation, and, in many

cases, innovations can be introduced into

the market more rapidly, Conservative design practices, however, play a large role in

determining which device will be selected

for mass production

STORAGE DEVICES

It is difficult to generalize about the

economies of scale of storage since the

‘ Ioth through 19th Steam Stat Ion Cost Survey,

E/ectrfca/ World, Oct 7, 1957, p 115, Oct 5, 1959, p

71, Oct 2, 1961, p 69, oct 7, 1963, p 75, Oct 18,

1965, p 103, Oct 16, 1967, p 99, NOV 3, 1969, p 41,

Nov 1, 1971, p 39, NOV 1, 1973, p 39, NOV 15, 1975,

p 51

value of storage is a strong function of the

cost of transporting energy and the strategy

of its use Many types of storage are constructed from moduIar units and do not

show strong economies of scale.

In most cases, low-temperature thermal

energy can be stored much less expensively

in large systems than in smalI storage tanks,

This is because the ratio of the surface area

required for a vessel containing a heated

fluid to the volume of the fluid stored decreases as the volume increases. A low ratio

means that less material will be required for

the storage vessel and that the area over

which heat can be lost to the environment

per unit of energy stored is reduced.

In some very large systems, no insulation

wilI be required other than dry earth. The advantage of large-scale storage of hot water

would be increased significantly if techniques for storing hot water in aquifers can

be developed. Taking advantage of this opportunity requires a piping network capable

of delivering fIuids to the central point.

Systems for storing energy at high

temperatures (e.g., above 300 OC/5720 F) typically consist of a large number of relatively

small modules, and large devices do not

show economies of scale. In many cases, the

storage must be located close to the site

where the energy will eventually be used.

For example, electricity can be “stored” in

bricks, heated to high temperature, which

are used to provide space heating for buildings during periods when electric rates are

high. Such devices must be located in the

buildings they serve.

No clear pattern of cost emerges for

devices capable of storing energy at intermediate temperatures.

Most of the techniques which have been

proposed for storing electricity in mechanical form (in hydroelectric facilities, for example) are only feasible in relatively large

units, although it may be possible to use the

numerous small dams which already exist

around the country for small amounts of

storage. Battery systems now available for

Ch. IV Onsite .E/ectric-Power Generation ● 121

I
122 ● Solar Technology to Today’s Energy Needs
Ch. IV Onsite Electric-Power Generation ● 723

storing large amounts of electricity for utilities are more economical in relatively large

units (several megawatt hours), although

economies of scale disappear long before

capacities equivalent to those of larg e

hydroelectric storage facilities are reached.

In the future, however, it may be possible

to develop low-cost batteries for which

there is no particular advantage in designing

units larger than a few hundred kilowatt

hours. This cannot be said for most other

types of chemical storage systems. Largescale storage of hydrogen or other gasses,

for example, can probably be best accomplished in large underground chambers.

The economies of scale of storage devices

is discussed in detail in chapter Xl.

Onsite or regional storage facilities also

offer a number of other advantages which

are not directly reflected in initial costs of

the systems. Table IV-2 summarizes the

benefits of centralized and decentralized

energy storage devices identified in an exam i nation of alternative techniques for storing electricity for utiIity use.

SOLAR COLLECTORS

Since most types of solar collectors consist of arrays of individual devices with individual areas less than 30 square meters

(m’), there is no clear economy of scale for

most types of coIIector arrays. An optimum

size for a heliostat central receiver system

will probably be established as the costs of

these systems are better understood, but it is

not clear whether a large penalty will have

to be paid if the system is not at the optimum size. Similarly, a system which requires

piping to connect a series of distributed

thermal collectors will probably have an optimum size since these plumbing costs will

become large for large systems.

Pond collectors and several other specialized collector designs may also show some

economies of scale up to 2,000 to 3,000 m2

,

but again, the penalty for building a smaller

system may not be large. Much more must

be known about the economics of collector

devices before confident statements can be

made in this area.

Table lV-2.— Impacts of Energy Storage on Electric Power Systems

Impacts Economic benefits*

Central Improved baseload capacity factor Low-cost charging energy

energy Conservation of oil, natural gas Reduced fuel costs

storage Reduction of spinning reserve capital cost credit ($20-40/kvv)

Higher reliability/reduced reserve margin Capital cost credit (to be determined)

More efficient load folowing Capital cost credit (to be determined)

Dispersed All of the above, plus: All of the above, plus:

energy 1.

storage

2.

3.

4.

5.

6.

Deferral of new transmission and Capital cost credit ($50-100/kW)

distribution lines

Deferral of substation reinforcement Capita l cost credit ($30-60/kW)

Misc. (transmission and distribution Capital cost credit ($10-20/kW)

loss, volt-ampere reactive control,

short circuit)

Increased security of supply/reduced Capital cost credit (to be determined)

reserve

Rapid installation (factory built) Reduced interest during construction

Modular/incremental capacity growth High capacity factor of storage

“Probable ranges; actual benefits dapaod on specific condhons in incfrvidual power systems.

SOURCE: F. R. Kalhammer, /rnpacrs of Energy Efficiency on E/ecfrk Power Systems, American Nuclear Society Meeting, San

Francisco, November 1975.
124 ● Solar Technology to Today’s Energy Needs

OTHER ASPECTS OF

CAPITAL COST COMPARISONS

The cost of equipment purchased for a

Iargeplant will always reflect the advantage

of discounts resulting from large purchases.

These savings occur because the manufacturer’s marketing costs and other overhead

costs are lower for large sales than for a

number of small purchases. Larger systems

may also benefit because there is no need to

perform detailed engineering for each installation, as may be the case for some onsite energy systems.

Taking advantage of the ability to best integrate an onsite generating system with the

climate and demand pattern at each site

could, however, add to the engineering cost.

Contractor overhead charges tend to be

slightly higher for smaller systems. Generalizations are difficult, however, since it may

be possible to develop standardized designs

for small systems.

Ease of rapid construction of small generating and storage facilities reduces the interest paid during construction —charges

which represent about 18 percent of the cost

of new electric-generating plants capable of

generating 1,000 MWe. 5 Rapid construction

also means that the effects of infIation are

easier to assess. Inflation occurring during

the construction of a 1,000 MWe generating

plant which wouId come online in 1983 is expected to represent about 30 percent of the

total value of the plant.6

Short construction times can also provide

much greater flexibiIity in meeting new

demands.

This advantage is particularly significant

when rapid fluctuations in the growth of demand make predictions difficult. Plants

which require only a month to construct require predictions to be accurate only a

month into the future. Moreover, a mistake

in forecasting is far less costly if the investment is limited. The economic benefits of

5 L$ ASH- 1.? JO Revised

‘ Ibid

large plants which require many years to

construct depend heavily on the accuracy of

demand predictions covering periods of a

decade or more. Utilities can react to unexpectedly low demand by delaying or deferring plant construction, but this process can

be costly–with the cost depending on the

amount of capital invested before the deferral. Forecasting mistakes can mean plants in

operation which are badly underutilized, yet

inaccuracies are inevitable given uncertainty about the future of energy supplies, costs,

and demands.

In the period 1973-75, demand did not rise

as rapidly as expected. Demand has fallen

far below the predictions and, as a result,

many utilities had far more capacity available than they could profitably employ. The

disastrous effect of inaccurate predictions

on the growth of electrical demand made

during this period was reflected in the

decline in load factors and a rise in gross

peak margins (see figure IV-4). Both features

indicate a serious underutilization of installed capacity, Utility commissions increased rates to permit these companies to

remain solvent (although in many cases the

utilities argued that these rulings still

preclude profitable operations).

Load factors for small systems (defined to

be the peak output potential of the generating system divided by the annual average

output) vary widely because of the erratic

nature of onsite energy demands. While

many large industries operate at virtually

full capacity throughout the day (and thus

have relatively constant electric and thermal demands), small industrial plants, commercial buildings, and residences can have

very uneven demands.

The irregular demands lead to relatively

poor utilization of the generating equipment. The problem usually diminishes as the

size of the total demand increases since

large loads typically are an aggregation of a

number of small loads. Unless the small

loads all change in unison, peak individual

demands will not all occur at the same time

and the ratio of peak to average demand
Ch. IV Onsite E/ectric-Power Generation ● 125

Figure lV-4.— Historic and Projected Load Factors of Utility Generating Facilities

L

I

Gross peak margin = ( installed capacity) - (peak demand)

I

(peak demand)

I

I

I

I

SOURCE 26th Annual Electrical Industry Forecast, ’ E/eclr/cal

wilI be less (This can be seen by noticing

that the load factors shown in table IV-3 increase with the size of the buiIdings served. )

Since the improvement is greatest when the

largest possible number of loads are connected, utility load factors are almost alWor/d, September 15, 1975, p 46

WASTE-HEAT

One major advantage of onsite generation of electric power is that an opportunity

is provided for making use of thermaI energy usually wasted by central electric-generways higher than onsite load factors, It is important to notice that this advantage is attributable to the size of the grid interconnection and not to the size of individual

generating facilities.

UTILIZATION

ating facilities. From 60 to 80 percent of the

energy consumed by conventional generating equipment is lost into the atmosphere

or nearby bodies of water, causing thermal
126 ● Solar Technology to Today’s Energy Needs

22 22

67 67

28.1

21.9

20.1

16.3

25.9

23.5

18.9

16,9

23.$

26.5

25.5

35.1

36.2

22

67

NOTE: The characteristics assumed for the buildings and heating and cooling

equipment used by the buildings are described in detail tn chapter IV of volume IL

In computing the ioad factors for industry, it was assumed that the facility

operated at 70 percent of peek capacity during active shifts and tttat the Dlant was

shut entirely for 2 weeks d“uring the year.

pollution in areas close to these plants. Approximately 17 percent of the energy consumed in the United States in 1972 was

wasted in this way and estimates show that

this fraction will rise to 25 percent by 1985,

when the United States is expected to be

more heaviIy dependent on electricity. 7

At the same time, enormous amounts of

steam are generated for space conditioning

and industrial processes. These applications

are inefficient uses of the fuel consumed

7 ERDA-48, Vol 1, appendix B

because the end requirement is generally for

a much lower grade of heat than the fuel utilized is capable of providing. The heat exhausted b y e Iectric-generation prime

movers can be used for many commercial

and industrial applications to produce an

overall efficiency of energy use in the range

of 70 to 85 percent. The implementation of

this technology could both reduce demands

for fuel and the demand for new capital in

the electric utility industry. (Both commodities are in short supply. ) It has been

estimated that if large-scale industries gen-
Ch. IV Onsite E/ectric-Power Generation . 127

erated al I of their own electric-power requirements by 1985 and served their process-heat requirements with waste heat,

where possible, the Nation would save 1,45

Quads* per year 8

Systems which make use of this “waste

heat” are conventionally called “total energy” or ‘‘ cogeneration” systems. A typical

system is shown in figure IV-5. Equipment

for total energy plants has been available

for many years, but use of such systems has

declined In 1972, only about 0.2 to O 3 percent of the U. S electric- generating capacity

made use of waste heat. g This decline has

resulted both from an overalI reduction in

onsite power and from the fact that electric

sales have been more profitable than steam

saIes 10 The use of large, remotely located,

electric-generating plants has, of course,

made thermal distribution unfeasible in

many cases. Total energy systems are still

widely used in Europe and the Soviet Union.

There is an enormous demand for thermal

energy in forms which are available from

total-energy systems In 1973, for example,

nearly 14 percent of the energy consumed i n

the United States went into space heating,

and 23 percent into industrial process

heat. 11

Analysis of the economic attractiveness

of both solar and nonsolar total-energy

systems depends on whether the overaII cost

savings (e.g. , the amount by which the savings i n electricity or fossil-fuel costs exceed

the cost of owning and operating heatrecovery units) will result in an acceptable

“ Energy I ndu~trlal Center Studv, op cit , pp 6, 7

‘ P R A( henb~ck and J B Cobel, $~te ArM/ysIs for

the Application of Total Energy .$}~tern~ to Housing

DPLe)opmentj, pre>ented dt the 7th I nter$oclety E nergy Convention E nglneerlngconference, San EIIego,

~al[t , Sept 25-29, 1972, p 5

‘“ Energy Industrial Center Study, op clt , p 21

) 1 M H Ross and R H Wllllarns, A $se~~~ng the Potential for Fuel Conservation, The I n$tltute for Publ IC

Po] I( y Alternatives, State Unlverjlty of New York,

Al bdny, N Y , July 1, 1975, p 19

rate of return to an investor, I n both cases,

the issue depends crucially on the balance

between thermal and electrical loads.

Total energy is not commonly used in

residential applications because of the large

daily and seasonal variation in thermal

loads, In spring and fall, for example, there

is a far smaller demand for thermal energy

than during the winter and summer months.

In the high-rise apartment studied in this

assessment, for example, the ratio between

energy required for electricity and the

energy required for heating and hot water

varied from 0.21 in January, when the

heating load was maximum, to 1.5 during

the spring and fall, when the primary requirement for thermal energy was hot water.

Only about 5 percent of the 550 total energy

plants operating in the United States in 1972

were installed in residences. The Department of Housing and Urban Development

(HUD) is, however, conducting a large field

experiment (MI US) with a total energy

system serving a mixture of residential structures and commercial facilities.

Total energy or cogeneration systems are

Iikely to be relatively more attractive in sites

where there is a consistent demand for heat.

Buildings such as laundries, hospitals, and

the food, paper, refining, and chemical industries are prime candidates. Most of the

large factories can be expected to operate

on a three-shift schedule, permitting maximum utilization of the generating facilities,

Many of the industries described use electricity in ratios amenable to cogeneration

and can use steam at temperatures which

can be conveniently supplied with cogenera -

tion systems. The precise demands of

buildings and industries of various types are

discussed in greater detail in the section on

“model building and industrial loads. ”

Some care should be exercised in usin g

the ratios which are developed for contemporary buildings and industries, since the

thermal and electrical demands coul d

change dramaticalIy as the resuIt of conservation techniques and new technologies.

Widespread use of electric automobiles, for
128 ● Solar Technology to Today’s Energy Needs

Figure lV-5.—Components of a District Heating System in Sweden

Fossil boiler

or

solar heater

2 Waste heat mains I

4 Units in individual homes

,

(4) Consumer service

unit for private house

(5) Large substation

in a school

SOURCES Figures (1) (2), (4). and (5) from “Dlstr{cl Heating” Teknlska Verken I Llnkop[ng AB [Sweden) Figure (3) from Margen, P H (Manager Energy

Technology Dlvislon, AB Atomenergl, Studsvlk R&D center, Sweden), ‘“The Future Trend for Dlstr{ct Heating, ” page 68, presenteci at the

Swedish Symposium on Combined Dlstrlct Heating and Power Generation Feb 2528, 1974
Ch. IV Onsite Electric-Power Generation ● 129

example, wouId increase the ratio of electric and heat recovery units could reduce therto thermal demand in residential buildings, mal demands,

OPERATING COSTS

Concerns about operating costs hav e

been a major barrier to onsite equipment in

the past, and badly designed systems have

been plagued by expensive maintenance.

Reliable data about the cost of operating

smalI systems designed for continuous-power output are extremely difficult to obtain

because of the smalI number of installations

in most of this size range. A summary of information from a variety of sources is shown

in table IV-4.

The greatest variation in the data occurs

in the small size ranges, where some of the

numbers are based on estimates made by

designers, some represent attempts to operate systems designed for “backup power”

operation in a continuous operation mode,

and some are averages of widely varying

operating experience. For example, the military standard for generator sets shows an

engine Iife of 2,500 hours for 15 kW units

and 4,000 hours for 100 to 200 kW units. 2

Daimler-Benz reports up to 20,000 hours of

engine life for its 10 kW engine.13 Operating

cost wilI depend strongly on the installation,

the skill of the operators, and the system

design. In most cases, it will be extremely

difficult to predict operating costs unti l

some experience has been obtained with the

particular application.

There is considerable variation in operating costs of larger powerplants (see figure

IV-6), and it is difficult to choose a single

number for comparative purposes. This is

particularly true for nuclear plants, where

experiences vary greatly and statistics on

long-term operating costs are cliff i cult to obtain. It is interesting to note, however, that

over half of the operating expenses of coalfired plants are due to the cost of operating

the boilers. Presumably, these costs would

be eliminated in a solar system that did not

rely on fossil backup, although the cost of

maintaining the collectors would probably

compensate for this savings.

RELIABILITY

Concerns about reliability have been a

major impediment to onsite power generation. Onsite installations can, in principle,

be made as reliable as utility power—or

more reliable if enough redundant units are

purchased or great care is taken in design

and manufacture. In fact, redundant onsite

power systems are occasionalIy used to provide realiable power when utility power is

“ Mllltary Standard, E Iectrlc Power Engine Cenerator set, Family Characterlstlc Data Sheets, M/l- Std633 A(MO), Oct 8, 1965 (Data provided OTA by the

Aerospace Corporation )

not sufficiently reliable. Achieving high

reliability with redundancy is, of course, expensive (see table IV-5). It is possible,

however, that a simple, mass-produced heat

engine could be designed to operate with

the reliability of a household refrigerator

(which is a simple heat engine operating i n

reverse). Designers working on a variety of

different onsite systems feel that this is not

‘ ‘ Mercede~-Benz Diesel and Gas Turbine Catalog,

Vol 36 (Data provided to OTA by the Aero$pace Cor -

poration )
130 ● Solar Technology to Todav’$ Energy Needs

Table IV-4. —Operating Costs of Various Systems

operating and

maintenance

Design type cost (c/kWh) reference

A. Small systems (5-50 kW)

—gas turbine 1.25 1

— diesel engine 0.4-2.4 2

— Stirling engine 0.74 3

—free-piston Ericsson 0.10 4

— air-conditioners 2-4 5

B. Intermediate systems (50-1,000 kWe)

—gas turbine 0.1-0.3 6

—gas turbine 0.25-0.4 7

—diesel engine 0.23 8

—diesel engine 0.27-0.55 9

—diesel engine 0.4 10

— gas engine 0.2-0.4 11

C. Larger systems (1 MW and larger)

— large diesel plants 0.33 14

— new coal-fired turbines 0.12 13

— new nuclear plants 0.3 13

Notes for Table IV-4.

1. International Harvester, Sofar Oivrsion, private communication, Marti 1976.

2. wm2,~-10.~hwm&~w~auis (astimatebasedcm combination ofdatafrom Allis Chalmers, Oatroit Oiesel,

and Dalmler-Benz) assummg 30 percent of mlt!al cost ($400/kW) IS revested m each overhaul,

3. A% Program Review; ‘Qwrtparafive Assessment of Orbital and Terrestrial Central Power Systems”’ (Interim report), March

1976, p. 31. (Assumes a 15.year hfe and 1 man-how every 3 months.)

4. Est!mate by Glen Benson of Energy Research and Generation Corp., private communlcatlon, November 1976.

(Assumes 1 mart-hour per year for,mamtenance.)

5. wonmaintenancecontractson2-tonairconditionerswf'tich areassumecf tooperateatpeak load--2 .000hoursperyear.

Su&I contracts are sofd by Seam for $60-$120/year (depending on the age of the system). It is assumed that an awcondi!tonlng cycle, operating m reverse as a heat engine, IS 17.percent efflctent,

6. MIUS T~nofogy Evaluation: “Prime Movers ORNL-HUO-MIIJS.1 l,”’ April 1974, p. 14.

7. Internahonal Harvester, Solar DivisIort, private commumcatlon, May 1976.

8. LXesel Engmeermg Handbook, 1966( inflated by 6 percent for 10 years)

9. “MIUS Prime Movers,” OP. CII., p. 21.

IO, Assumes 30 percent of capital cost (assumed to be $300/kW) IS Invested for each 30,000 hours of operation.

Il. “MlUS,” Op. Clf., P. 14.

12. ‘<Statistics d Privately owned Electric IJtilifies in the United States,” 1974, FPC, pp. 36, 37, and 21.

13. VOth Annual Sfeam Station Cost Survey,” E/ectr/ca/ Worfd, November 15, 1977, p. 46.

14. Morgan, Dean T. and Jerry P. Daws, “High Efficiency Decentralized Electrical Power Generation Utlllzlng Dtesel

Engines Coupled with Organic Working Fluld Ranklne-Cycle Engines Operahng on Diesel Reject Heat,” 1974,

pages 5-45, (Assuming a 60 percent load factor.)
Figure IV-6. —Annual Operating Costs Versus Equivalent Full-Power

Hours of Operation for Baseload Plants

(6) insurance

(Fuel cost excluded)

●

●

Table IV-5. — Engine Requirements for Systems

Designed to Provide Reliability

Equivalent to Utility Power Reliability

(Approximately 5 hours of outage per year, including

failures in generating, transmission, and distribution

equipment)

Fraction of

Number of peak load which Reliability

engines in can be met required of Relative

system by each engine each engine cost’
132 Ž Solar Technology to Today’s Energy Needs

ample, have a “mean time between failures”

of about 500 hours, 4 Diesels and gas turbines, in the range of 50 kW to 1 MWe, however, average 1.2 years between failures. 15 16

Gas turbines typically operate 20,000 hours

(2.3 years) without overhauls, even in instalIations where they must operate unattended, and 40,000 hours between failures

have been experienced on some systems. ”

prototype Stirling engines have operated

10,000 hours without failures in bench testing .

18 Free piston Ericsson-cycle devices, if

designed properly, should be able to operate

with very high reliability because of their inherent simplicity, the small number of moving parts, and the fact that no seals around

rotating shafts are required. The reliability

of diesel equipment depends on whether the

system has been designed for continuous

‘

 4 M/US Technology .E valuation: Prime Mo~ers,

OR NL-HUD-MIUS-ll, April 1974, pp 57-60

“ Ibid

“ M Gamze “A Critical Look at Total Energy

Systems and Equipment, ” Proceedings, the 7th Annual

I ECEC Conference, San Diego, Callf , Sept 25-29 ,

1972, p 1266

17 Robin Mac Kay, “Generating Power at High Eftlclency, ” Power, June 1975, p. 87

‘“ R C Ullrich (North American Philips Corporation), private communlcatlon, October 1976

operation and on the revolutions-per-minute

(r/rein) of the device. Low r/rein systems

which are designed for continuous operation can typically require one relatively inexpensive overhaul, costing about 10 percent of the initial investment each 10,000

operating hours, and a major overhaul costing 20 percent of the investment each 20,000

operating hours. Almost all reliable data

deals with systems larger than 50 to 200 kWe

and Iittle data exists for very smalI systems.

Standards for reliability cannot be measured in any systematic way. Requirements

will differ from customer to customer. Some

industries, for example, would face catastrophic losses if they lost power for an extended period (say several hours), while

residential customers might not be willing to

pay a premium for extremely high reliability.

One of the disadvantages of providing

power from a centralized utility grid is that

all customers must pay for a high system

reliability whether they need it or not. Onsite generation would permit much greater

flexibility in this regard.

Utilities currently try to maintain enough

capacity to ensure that failure of the generating plant will curtail power for no more
Ch. IV Onsite Electric-Power Generation ● 133

than 2.4 hours per year. (This is a typical

working figure, but standards vary. Southern

California Edison Company, for example,

uses a standard of 1 hour in 20 years ) 19 It

has been argued, however, that this standard

for generating reliability is too high, and

that the last few hundredths of a percent of

reliabiIity are enormously expensive, 20 particularly since the transmission and distribution system is usually less reliable than the

generating plant The effect may not apply

to all utilities, however, and optimal expansion plans may welI result in maintaining

very high reliabilities in some instances.

Analysis of the requirements of different

types of customers in this regard is almost

nonexistent It is difficuIt to anticipate how

much different customers wouId be wiIling

to pay for reliability If they were given a

choice The costs of providing high-reliability service could be reduced, for example,

if the customers were wi I I Ing to accept lower reliabilities during predictable periods —

such as during peak-demand hours — or during maintenance cycles

The requirement for providing high

reliabiIity with onsite equipment can be relaxed considerably if the utility grid can be

used to provide complete ‘‘backup’ when

failures occur or when systems are disassembled for routine maintenance The impact of

providing this backup power on utility costs

is a complex issue and cannot be treated in

detail in this paper

It is clear, however, that a small number

of customers requiring backup would not

have a major impact on utility operation,

and that a large number of customers with

small backup requirements wouId not pose

a problem since failures would be distributed at random, Some correlation with

peak-demand periods could be expected

(Solar outages due to variations in sunlight

wouId, of course, be correlated, but failure

of equipment should be similar to other

types of onsite failures, ) A small number of

very large users wouId, however, pose a

serious problem if they depended on utilities for complete backup. I n such cases,

provision would have to be made for drastic

reduction of onsite demands whenever the

onsite generating equipment failed. The

presence of electric storage, either onsite or

in the utility grid, could do much to alleviate

the problems of unanticipated equipment

failure

I t seems, therefore, that onsite equipment

can provide any desired level of reliability If

a premium is paid, if the utility is used to

provide backup power, or if the optimistic

expectations of system designers are realized, Existing equipment can provide a very

high level of reliability without redundancy,

although the exacting standards of utility

power cannot be matched, The seriousness

of this f a i I u re wou Id have to be judged o n a

case-by-case basis, Unfortunately, there is

little operational experience for most promising onsite equipment, and basic long-term

concerns are unlikely to be finalIy resolved

before an adequate base of experience with

these systems has been developed
134 ● Solar Technology to Today’s Energy Needs

variety of local and nationally based groups

have legal standing orders to contest siting

plants and rulings.

Most small plants would be required to go

through many of the procedural steps required of the larger plants, and less effort

may be required to justify the installation of

a single large plant in a remote area than to

justify several small facilities in areas where

local protest would be Iikely to develop. On

the other hand, the onsite generating equipment might face far fewer objections than

the large sites for a variety of reasons:

● Each plant would be relatively small,

and the impact on the local environment would usualIy be sIight.

● I n the case of cogenerat ion and total

energy systems, energy would be required onsite for heating and industrial

applications, even if no electricity were

generated onsite, and thus the incremental impact of equipment and emissions traceable to electric generation

wou Id be small,

It could be plausibly argued, in most

cases, that the impacts of alternatives

to onsite generating facilities would be

more severe than those imposed by the

on site design.

Onsite facilities would not require a

major dislocation of populations, no

construction camps would be required,

no new roads or new waterways would

be necessary, etc.

Large solar-electric systems, which require large amounts of land in a single area

for collectors, could also face serious siting

problems. Smaller onsite solar systems,

which could be integrated into the buildings

or immediate region being served with solar

energy, wouId undoubtedly face far fewer

objections,

MISCELLANEOUS OPERATING PROBLEMS

A major constraint to onsite power generation has been the reluctance of owners and

managers of companies other than utiIities

to accept the burden of owning and operating complex electrical generating facilities; there has been great apprehension

about maintenance costs, reliabilities, personnel requirements, and other technical

uncertainties.

Operators of most commercially available generating equipment require extensive

training, and in many jurisdictions, local

codes set specific standards. For example,

the District of Columbia requires operators

of high-pressure steam systems, capable of

generating more than 55 kW of thermal

power (equivalent to about 15 kW of electric power) to hold a “second-class steam

engineer’s Iicense. ” Obtaining such a license

requires 3 years of experience with steamplants having pressures greater than 15 psi

and passing a special examination.21

Thus, qualified operators are difficult to

find and they command high salaries. Several steam-system owners have indicated

fear about their vulnerability to losing a

chief engineer with unique experience.

Equipment has also been a problem; the

market for onsite equipment is so small that

little new design work has been done, Existing onsite generating instalIations are

nearly all “one-of-a-kind” designs; they are

often installed by engineers who do not

have much experience in the area, and they

frequently use equipment in ways not originally contemplated by the manufacturer. As

a result, performance has often been disappoint ing.22

21 “Operation and Maintenance of Boilers and

E nglnes and Licensing of Steam E nglneers, ” District of

Co/urnbIa Register, Washington, D C

“ Maurice G Gamze, “A Critical Look at Total

Energy Systems and Equipment, ” Proceedings, the i’th

Annual IECEC Conference, San Diego, Callf , Sept

25-29, 1972, p 1266
devices eliminates one of the major impediments to conventional onsite equip -

ment — their use of relatively expensive Iiquid and gaseous fuels Table IV-1 indicated

that fuel costs dominate the cost of providing power from smalI generating equipment even at current fuel prices I n man y

cases, however, it may be attractive to try to

provide backup for a solar-powered facility

by burning a fuel during periods when solar

energy sources are not available. It may be

possible to develop boilers for small devices

compatible with coal, waste products, and

other “biomass” fuels The development of

fluidized-bed boilers of various sizes may be

particularly attractive for such an application. The development of such systems

would, of course, also increase the attractiveness of onsite generating devices operating entirely from energy sources other

than direct solar energy

Figure IV-7. —Space Requirements of Typical Combined-Cycle Plants
Chapter V

THE RELATIONSHIP BETWEEN

ONSITE GENERATION AND

CONVENTIONAL PUBLIC UTILITIES
Chapter V.–THE RELATIONSHIP BETWEEN ONSITE

GENERATION AND CONVENTIONAL PUBLIC UTILITIES

Page

Background . . . . . ........................139

Electric Transmission and Distribution .. ....141

Thermal Transmission and Distribution . . . . . .143

Sale off PowerGenerated Onsite . ...........144

Metering ....., . . . . . . . . . . . . . . . ... ... ...144

Safety . . . . . . . . . . ......................144

Quality of Power Fed Back to Utilities .. ...145

Local Distribution Capacity .. .. ... ... ....145

Economic Dispatch. . . . . ................145

Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....146

Time-of-Day Pricing. . . . .................146

Storage Strategy . ......................147

Load Management. . ....................147

Offpeak Electricity . ....................148

Ownership . . . . . . . .......................148

Utility Attitudes . . . . . . . . ................150

The Cost of Providing Backup Power From an

Electric Utility .. .........................151

Backup PowerWithEnergy SourcesOtherThan

Electricity . . . . . . . . ...................159

AppendixV-A.– Analytical Methods. . . .. ....161

LIST OF TABLES

Table No. Page

l. A Comparison of the Cost of Transmitting

and Distributing Energy in Electrical,

Chemical andThermal Form . . . . . . . . . . . .

2. Construction Expenses of Electric

Companies . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. District Heating Systems . . . . . . . . . . . . . . .

4. The Capital lntensityof Major U.S.

Industries . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5. The Fractional Difference Between the

Utility Costs[¢/kWh] Required to Provide

Backup Power to the Systems Shown and

the Costs to ProvidePower to a Residence

EquippedWith an Electric Heat Pump . . . .

6. Levelized MonthlyCosts for a Well-lnsulated Single Family HouseShowing the

Effect of Marginal Costing for Backup

Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

140

142

143

149

153

154

Table No. Page

7. Ratio of Price Utilities Can Pay for

Solar Energy Generated Onsite to the

Price Charged by Utilities for Electricity. ..155

8. The Fractional Difference Between the Utility

Costs Required To Provide Backup Power to

the Systems Shown and the Costs of

Providing Power to a High Rise Apartment

Equipped With Central Electric Air-Conditioning, Electric Hot Water, and Baseboard

Resistance Heating. . ..................156

9. The lmpact of Offpeak Storage on Utility

costs . . . . . . . . . . . .....................157

IO. Levelized MonthlyCosts for a Single Family

House Showing the Effect of Marginal

Costing and BuyingofOffpeak Power ....158

11. Leveiized MonthlyCosts of Several Kinds of

Energy Equipment in a Single Famiiy Detached Residence in Albuquerque, N. Mex.160

A-1. Average Characteristics of PrivatelyOwned

Utilities in 1974 . ......................163

A-2. Numbers of Buildings in “Typical’’Utility

Modeled WhichUseHeating and Cooling

and HotWaterEquipment . .............163

A-3. industrial Load Profile Used..... . ......164

A-4. Characteristics of Equipment Used in the

Utility Model.... . .....................170

A-5. Assumptions About the Nonconventional

Systems Used in the Utility lmpact

Analysis . . . . . . . . .....................170

LIST OF FIGURES

Figure No. Page

l.improvement in the Pattern of Electricity

Consumption in England’s Southwestern

Electricity Board Resulting From a Shift

to Time-of-Day Electricity Rates . .........146

A-1. A Typical Load-Duration Curve for an

Electric Utility . ........................162

A-2, Ratio of PeakDemands to Average

Demands as a Functionofthe Standard

Deviation of ’’Wake-Up’’Times . ..........165

A-3. Hourly ’’Miscellaneous” Electric Load

Profile for Single Family House With

DifferentTypes of Diversity . .............166

A-4. inverted Load-Duration Curve of a

Typical Electric Load. . . . . . . . . . . . . .......168
Chapter V

The Relationship Between Onsite Generation

and Conventional Public Utilities

BACKGROUND

The value of onsite energy systems cannot be addressed by examining

their performance as isolated systems. While it is possible to construct onsite solar devices capable of operating with no connection to other power

sources, it is seldom economically attractive to do so when other sources of

power are available.

It is tautological that designing an optimum approach for providing energy

in a given region requires that all equipment for installing and consuming

energy be considered as components of a single integrated energy system

designed to meet a fixed set of energy demands: maintaining building interiors at comfortable temperatures, providing lighting, supplying heat for industrial processes, etc. Any attempt to simplify the problem by considering

the capabilities of components in isolation must result in a less efficient outcome. Moreover, it is likely that without taking this synthetic perspective,

some critical aspect of the overalI system will be neglected.

Performing this kind of analysis is difficult because of the complex and

highly interdependent energy systems which have emerged over the past few

decades, the variety of equipment which is currently in use, and the bewildering variety of devices now u rider test and development. This chapter provides

a perspective on some of the major issues confronted in integrating onsite

systems into larger systems for supplying energy and provides the basis for

making realistic estimates of the cost of operating onsite equipment.

The design of an optimum energy network

which includes onsite solar facilities requires choices in the following areas.

. How much of the backup energy shouI d

be supplied from energy storage equipment, and how much backup energ y

should be supplied from convention I

energy sources? (This usually transIates

into determining the opt i m u m size for

onsite storage equipment )

●

●

●
140 ● Solar Technology to Today’s Energy Needs

If it is possible to transmit energy inexpensively, overall energy costs can usually be

reduced by connecting together as many

energy consumers as possible. If onsite generating systems are not connected, each

generating unit (solar plus backup) would

have to be large enough to meet the peak

demand of the building or industrial process

which it is designed to serve. The load factors of individual buildings are usually very

unattractive (see table V-1 ). Onsite load facTable V-1 .—A Comparison of the Cost of Transmitting and

Distributing Energy in Electrical, Chemical, and Thermal Form

Capital

cost

$92/kW

(4)--

NOTES: I

1 A ~apltal ,ecoveV factor Of O . I 5 is used to calculate annual caPital

charges.

2Assumes a capacity of 2,500 MW Ior one 765 kv line.

3Utility construction expenditures of $1,7 billion in 1975 for 3,762 ad.

ditional miles or S461,000 per mile average. (Statistlca/ Yearbook of

ffre Electrlc Utl//ty Industry for 1975, Edison Electric Institute, New

York, N.Y , Oct. 1975.)

4 The 1970 Natlona/ Power Survey, Federal power Commission,

Washington, D. C., p. 1.13.8, Dec. 1971.

51nvestor.owned electric utilities spent approximately $851J million on

transmission O & M costs in 1975 for 1.5x10’Z kWh. (S fahstlca/ Year.

book of the E/ectrlc Utjllty /ndustry for 1975).

6Assume$ an end.use efficiency of 100 percent

7Nat,ona/ Gas Survey, u,S Federal Power COmmisS.iOn, VOI. 1, P. 34.

1975.

8AII natural gas companies spent $53 I million in 1976 for 1,845 miles

of new transmission pipeline or $287,000 per mile average. (7976 Gas

Facts, American Gas Association, Arlington, Va., 1977).

9 Four percent of total natural gas consumed was used for PiPeilne

fuel In 1976 This is equally allocated to transmission and distribu.

tion. (AGA Gas Facts).

IONatlona/ Gas Survey, U.S. Federal Power Commission, VOI. Ill, P. 129,

1973.

11 All natural gas Utllilles spent $1 1 billton in 1976 on o & M for

transmission for 148 trillion cubic feet (TCF).

12ASSumeS end.use efficiency Of 65 Percent

13tLResidential Energy Use to the Year 2(toO: Conservation an d

Economics,” Oak Ridge National Lab, Report ORNIJCON.13, Oak

Ridge, Term., Sept. 1977,

141nyestor.owned electric utilities spent S2.8 bdlion on COn StrlJCtiOfl Of

distribution facilities for 21,700 kW of new capacity in 1975.

(Statlshcal Yearbook of the E/ectr/caf Ut///fy /rrdustry for 7975.)

151nvestor.owned utilities spent approximately $1.59 billion in 1975 for

distribution O & M costs for 1.5x10’2 kWh. (Statistlca/ Yearbook of

the E/ectr/ca/ Utl/lty Industry Iof 7975.)

16 Calculated from the average cost of S400 per customer (Private

communication—American Gas Association) with an average hot

water and space heating requirement of 36.4x10] kWh (121 MCF) per

year and an assumed load factor of 0.4.

17AII natural gas utilities spent S1.1 billion on distribution 0 & M In

1976 for 14.8 TCF (AGA Gas Facfs),

18 See volume Il.

19 f1Evaluation of the Feasibility for Widespread Introduction Of COal in.

to the Resldenttal and Commercial Sectors. ” Exxon Research and

Engineering Co., Linden, N. J., Vol. 11, p. 6.11, Apr. 1977. These two

studies give a construction cost of about S14 milllon for the size

system in question, which requires a peak capacity of 70,000 kW, as

shown by reference in note 20.

20 Annua\ o & M costs are calculated by assuming they are 3 Percent

of capital costs, which is the average of the percentages for gas and

electric systems.

21 The cost of energy lost in transmission was estimated usln9

0.04c/kWh for electricity y and 1.5c/kWh for thermal energy,
Ch. V The Relationship Between Onsite Generation and Conventional Public Utilities ● 141

tors can be as low as 15 percent, while typical utiIity load factors are 50 to 60 percent.

Moreover, each onsite facility would have

to provide enough redundant equipment to

achieve acceptable levels of reliability. If an

interconnection is avaiIable, however, it is

necessary only that the combined output of

all generating units in the system be able to

meet the aggregate peak demand of the region. The aggregate peak will be lower than

the sum of the individual peak demands

since individual peaks will occur at different

times (this is usualIy called “diversity” in the

demand). The advantage of the connection

is magnified by the fact that most generating devices operate less efficiently when

operated to meet an uneven demand. Interconnections also permit greater freedom in

selecting generating and storage equipment

(onsite and centralized facilities can be

selected as they are appropriate), and it is

easier to optimize the efficiency of the total

system throughout the year by controlling

the performance of each system in the network in response to the total load.

The problem of uneven loads is a particularly difficult one in the case of electric

utiIities since generating and storage equipment tends to be extremely expensive, although chemical and thermal transport systems can also benefit from balanced loads.

It may prove feasible, for example, to pipe

hot water generated in collectors located on

a number of separate buildings to a central

thermal storage facility, If this storage facility is large enough, collectors need only have

an annual output large enough to provide

for heating and hot water requirements and

storage losses. Such systems may require

less collector area per building unit than

conventional solar heating and hot water

systems using relatively small amounts of

storage.

While connecting energy generating and

consuming devices into a single energy network can lead to significant savings, the

transmission and distribution systems required can be extremely expensive. The

costs of several types of energy transport

systems are summarized in table V-1. Comparisons of this type can be somewhat misleading because costs will vary greatly from

site to site, but the table at least allows a

crude ranking of alternatives. It indicates,

for example, that transporting energy in

chemical form is by far the least expensive

approach. It is interesting to notice, however, that distributing energy in the form of

hot water over distances of 1 to 2 miles is only about 30 percent more expensive than

transmitting electrical energy over typical

distances from generating facilities to consumers, I n this comparison, no attempt was

made to share the cost of the trench dug for

the hot water pipe with potable water,

sewer, telephone, or other Iines which could

be placed in the excavation, The electric

distribution costs would have been significantly higher if buried cables were used.

ELECTRIC TRANSMISSION AND DISTRIBUTION

Electric transmission and distribution is

an expensive undertaking. Over half of the

capital invested by electric utilities in the

United States is invested in a massive network of transmission and distribution equipment. In recent years, the ratio between

capital investment in electric generating,

IStat/st/cs of Pr/\ate/y Owned E/ectr/c Ut///eses in the

Un/ted States, Federal Power Commlsslon, 1974, p 40

transmission, and distribution equipment

has fallen because of the rapid increase in

the cost of generating plants [see table V-2),

Each dollar now invested in generating

equipment is accompanied by a 16-cent investment in transmission equipment and a

23-cent investment in distribution systems,

The high cost of the electric transmission

and distribution system is due in part to the

fact that the lines have relatively low load
142 ● Solar Technology to Today’s Energy Needs

Table V-2.—Construction Expenses of Electric Companies

1965 1967 1969 1971 1973 1975 1977

Total Investment (billions of

dollars) . . . . . . . . . . . . . . . . . . . . . 4.03 6.12 8.29 11.89 14.91 15.09 19.50

Production equipment (%). . . . . 32.3 41.7 46.1 56.3 58.9 65,1 68.3

Transmission equipment . . . . . . . 23.3 21.5 18.7 15.2 13.7 11.5 10.7

Distribution equipment. . . . . . . . . 39.4 32.3 29.2 23.3 22.6 18.7 15.7

Other . . . . . . . . . . . . . . . . . . . . . . . . 5.0 4.4 4.0 5.1 4.8 4.7 5.03

SOURCE. EBASCO 1977 Business and Economic Charts (Ebasco Services, Inc., New York, NY. )

factors. Hot water and steam distribution

systems used for heating buildings typically

have load factors of 33 percent (see table

v-1 ).

The electric transmission and distribution

lines now in place are typically 90-percent

efficient, but it is hoped that improved

technology will lead to overall efficiencies

of 92.5 percent by the year 2000. 2 The improved efficiency, however, will most likely

add to the capital cost of the systems. Gas

pipelines are typically 90-percent efficient,

the losses being due primarily to the fact

that gas is withdrawn to run pumps in the

pipeline. 3 No comparable information is

available on the efficiency of hot water and

steam transport systems. Losses are a strong

function of the ground and fluid temperatures, the distances traveled, and the average size of the pipelines. Some recent steam

distribution systems, however, have experienced losses on the order of 15 to 20 percent

and have created serious difficulties for the

systems relying on them.4

‘ERDA-48, Volume i, pp. B-10 and B-n, 1975.

‘American Gas Association.

‘American Public Power Association, private communication, November 1977

The cost of maintaining transmission

equipment can also be substantial. In 1974,

the cost of operating and maintaining the

network of electric transmission and distribution lines owned by privately owned utilities in the United States exceeded the cost

of operating and maintaining the generating

facilities (fuel costs excepted). ’ Annual

maintenance costs for a smalI hot water distribution system can amount to about 3 percent of the initial capital cost of the equipment.

6 Maintaining steam systems may

prove to be significantly more expensive.

In addition to direct costs, transmission

Iines can have serious environmental consequences. It is estimated that over 3 million

acres wilI be required for new transmission

lines by 1990. ’ Much of this construction

will occur in scenic areas where opposition

is likely. In addition, it is possible that the

large electric fields produced by high voltage transmission lines may be harmful. The

question is being investigated and the results are inconclusive at this time.

‘Statistics of Privately Owned Electric Utilities in the

United States, op. cit , pp. 35, 39,40, 42,43.

‘W. R. Mixon, et al., Technology Assessment of

Modular Integrated Ut;//ty Systems, Oak Ridge National Laboratory, ORNL/HUD/MIUS-25, pp 3-189 and

3-190.

7Thermo-E Iectron Corporation.
Ch. V The Relationship Between Onsite Generation and Convention/ Pub/ic Uti/ities ● 143

Table V-3.—District Heating Systems

District Heating Systems in the United States

44 city systems

Total steam sold (millions of pounds). ., . . . . . . . . . . . . . . . . 84,246

Total steam delivered to system (millions of pounds) . . . . . . . . . 96,672

Annual system load factor . . . ., . . ., ., . . . . . . . . . . 33%

Number of customers (in thousands) . . . . . . . . . . . . . . . . . . . . . . . . . 14,903

Length of distribution system (in miles) . . . . . . . . . . . . . . . . . . . . . . . . 573

Installed air-conditioning (tons) . . . . . . . . . . . . . . . . . . . . ... , . . . . . . . 666,051

New York

32,702

38,469

37‘A

2,514

100

569,945

Note New York City has the largest American system, selling nearly 10 billion kWh per year The load Is 30 percent residences. 45 percent

office bulldings, 11 percent industrles and 13 percent institutions.

SOURCE Offlcial Proceeding, 80th Annual Meetlng of the International District Heating Asscciation, June 1969, pp. 22-30, quoted on p 24

of ORNL-HUD-19, Ibid

District Heating Abroad

Sweden Denmark W. Germany U.S.S.R.

(1973) (1973) (1973) (1971 )

Energy sold for district heat

(millions of kWh) ... . . . . . 12 14 38 1,100,000

Units connected . . . . . . . . . . . . . . . . . . 600,000 30% of dwellings 83,000 75%

SOURCES I G C Dryden, The Eff/c/enf Use of Energy, IPC Science and Technology Press, 1975, p 359

Quoted In Teploengetika, Vol 18, No 12, 1971, pp 2-5

W Hausz, and C. F Meyer, Energy Conservation Is the Heat Storage Well the Key?” Puh/Ic Uf,/,tfes Fortn,ghfl} APrIl 24 1975

THERMAL TRANSMISSION AND DISTRIBUTION

Most hot water and process steam is consumed close to where it is generated, but a

number of cities have systems for distributing steam to residences and industries. I n

the United States, many older systems have

been abandoned, and few new systems are

being built. The Modular Integrated Utilities

System (MI US) in Jersey City, N. J., is one of

the few recent exceptions to this trend. The

abandonment of steam distribution is due

mostly to the overalI decline of onsite generation. This tendency is reinforced by the

fact that many older steam-distribution systems were not designed to return water to

the generating plant, as the turbines operated on untreated water. This procedure became impractical with the addition of large,

high-pressure, steam-generating facilities requiring expensive water purification systems. Table V-3 estimates the capacities of

district heating in the United States and

abroad. On the other hand, district heating

has been used much more extensively in

Europe. For example, 30 percent of the residences in Denmark are connected to district

heating systems. Sweden estimates that 70

percent of its multifamily units and 20 percent of its single family homes will be connected to district heating systems by 1980.

West Germany plans to provide district heat

to 25 to 30 percent of its dwellings by 1980,8

81 G C Dryden (ed ), The Eff/c;ent Use of Energy, IPC

Science and Technology Press, 1975, p 358.
144 ● So/ar Technology to Today’s Energy Needs

The feasibility of using district heating

systems depends much on the density of

dwelling units. A study conducted in connection with the MIUS project estimated

that a garden apartment complex in the

Philadelphia area (60 buildings with 1 2

apartment units per building) would cost

about $410 per unit for heated water distribution and $330 per unit for chilled

water,

9 A MIUS system was actually installed in Jersey City, NJ., for approximately

this amount.10 A preliminary estimate of the

cost of a large district heating system capa9G Samuels, et al , M/US Systems Ana/ysis, /n/t/a/

Cornpar/sons of Modular Sized /rrtegratecf Ufi/;ty Systems and Corrverrt;ona/ Systems, Oak Ridge National

Laboratory ORNL/HUD/MIUS-J une 6, 1976, p 144

IOPaul R Achenbach and John B Coble, Site Ana/-

ys;s for the App/;cat;on of Total Energy Systems to

Hous/ng Developments.

ble of serving a community of 30,000 people

in a mixture of apartments and single family

units indicates that the cost per unit for this

dispersed system would be nearly three

times as great, The ability of a system to

amortize these costs depends on the cost of

the energy supplied and the yearly energy

demand of each building. A rule-of-thumb

applied until recently in West Germany was

that a “break-even” housing density was one

which required 44 MWt

/km 2 for existing urban areas and 28 MWt

/ k m

2 for new developments. Recent increases in fuel prices,

however, have led them to consider areas

with demands as low as 14 MWt/ k m

2

. The

garden apartments in the MIUS study had a

demand of approximately 30 MWt

/km

2

.

1‘1 G.C Dryden, op clt , p 251

SALE OF POWER GENERATED ONSITE

METERING

No major technical barriers need to be

overcome in designing meters for onsite

energy equipment, but new types of meters

may have to be developed for this purpose.

If a utility owns onsite equipment with thermal output, some technique must be found

for billing customers for the energy produced by the onsite device. One utility has

suggested that the simplest technique would

be to bill a customer on the basis of actual

capital and maintenance costs, although

meters capable of measuring the energy

generated by solar thermal systems of

various sizes are available. 12 13 An electric

utiIity in Florida is using such Btu meters on

solar hot water heaters installed under its

auspices. 4

1‘Phi Iadelphla E Iectric Company In an interview reported In the General E Iectrlc study Conceptual De

sign and Systems Analysis of Photovolta;c Power Systems.

1‘For example, the E Iectron Advancement Corporation sells meters measuring 1400 to 1500 F water at

flow rates of 30 to 100 gpm at a price of $400 to $500

(price list Feb 9, 1977)

“So/ar Energy Digest, January 1977, p 9.

The metering problems of onsite electric

generating systems depend on the nature of

the customer’s relationship with the local

utility, If the utility is wilIing to purchase

energy at the same price as it sells energy to

onsite users (or if it owns the generating

equipment itself), it may not be necessary to

change metering systems — because conventional meters can subtract from the net

energy account when energy is being sold

and add to the account when energy is purchased. This practice is currently permitted

in several New England States on an experimental basis. ” In cases where energy is

sold at a different price from that purchased, dual meters will be required —with

one ratchet to read sales to the customer

and one ratchet to read purchases from the

customer,

SAFETY

There could be risks associated with the

installation of onsite electric-generating

“Ben Wolf, Gemini Company, private communlcatlon, Apr 27, 1977.
Ch. V The Re/atlonship Between Onsite Generation and Convention/ Public Utilities ● 145

equipment which would not automatically

disconnect from utility lines when repairs

are being made or when a utility Iine breaks

in a storm or accident. As one utility put it,

this “poses no problem for trained utility

crewmen who treat al I Iines as hot unless

locally grounded The major problem can

arise through exposure of laymen and children to potentially hot lines before repair

crews arrive on the scene “

16 This problem

can be eliminated if the onsite generating

equipment is automatically taken off the

line whenever the power fails. This is a

standard feature in at least one design of

smalI power-conditioning equipment now

on the market. 1

7 The utilities Interviewed in

the General Electric study indicated that

any type of onsite equipment which did not

incorporate such a feature could be fitted

with a device al lowing the utlIity to sever

the connection with the utility distribution

network through telemetry. Such units were

estimated to cost about $100. 18 (The same

units could also be used for interruptible

service and for load management ) It would

be necessary for the utility to approve the

onsite equipment connected to its grid in

order to ensure that adequate safety features of this type were installed

QUALITY

BACK

There shouId be

OF POWER FED

TO UTILITIES

no difficulty in constructing equipment capable of providing power

to utilities which meets utility standards of

voltage regulation and frequency control. 19

One manufacturer of small inverter systems

has sold 65 units which are integrated into

“Paclflc Gas and t Iectrlc Company Interview published In General E Iectrlc’s photovoltalc study cited

previously

‘ ‘Alan W Wilkerson (President of Gem[nl Com -

pany), Synchronous /n~ers/on Techrr/ques for Utilization of Waste Energy, 1976

‘‘Conceptual Des/gn and S ysterns Ana/ys/s of Photo-

\o/ta/c S ysterns, General E Iectrlc Corporation, Schenectady, N Y , Mar 19, 1977, pp 5-9

“General Electrlc Company, op clt , pp 5-4

utiIity systems, and quality of power has not

been an issue 20

LOCAL DISTRIBUTION CAPACITY

One potential technical difficulty, identified in the General Electric study, is the

possibility that onsite units which feed electricity back into the power distribution grld

would exceed the capacity of the Iines and

transformers serving the area It is unlikely

that onsite units would produce excess

power for sale at a rate high enough to exceed the peak purchases of the onsite customer. There could be some problems in

older communities, where distribution systems were installed without considering the

possibility that a substantial number of residences might be equipped with al l-electric

systems. A typical distribution system, however, should be able to accommodate the

output of residential photovoltaic systems

without major changes in transformers or

Iines.21

ECONOMIC DISPATCH

Electric utilities now control the scheduling of their generators via computer. This

optimizes the efficiency of their entire system on a minute-to-minute basis throughout

the day As long as a relatively small number

of a utiIity’s customers are using solar equipment which can generate electricity, n o

large-scale shift is necessary in curren t

economic dispatch practices. 22 The net load

to the utility would fIuctuate throughout the

day, but current equipment and management schemes are adequate to handle the

relatively large fluctuations that already occur with daily cycles, local weather variations, and industrial energy consumption.

The utilities interviewed by the Genera l

Electric Company indicated that special

dispatch strategies would not be required,

even if onsite generating devices were installed by 10 to 30 percent of their customers.

‘OGemlnl Company, op clt

“General Electrlc conceptual design study, pp 5-3

“General E Iectrlc conceptual design study
146 ● Solar Technology to Today’s Energy Needs

The Dow Chemical Company’s examination of industrial cogeneration was “unable

to identify any problems or potential problems of transient stability attributable to

dispersed industrial generation. The effect

of dispersed generation close to load centers is to improve system integration and

stability problems.”23 However, if dispatching or system stability became a problem,

the difficulty could be resolved by using the

interruptible service devices discussed earlier. When onsite users were producing too

much energy for a utility’s needs, the onsite

devices could simply be disconnected from

the load. (The cost of this could be included

in the $100 per unit cited for interruptible

services meters. ) It is also possible that

economic dispatch of electric utiIities could

improve if a number of onsite generating

facilities were equipped with sufficient onsite storage of a fossil backup system. Dispatch is not a problem for systems relying

on chemical fuels for backup.

CONTROL

TIME-OF-DAY PRICING

Some of the advantages of connecting energy generating and consuming devices with

a common energy transport system cannot

be realized if control over the equipment is

not exercised by a central authority capable

of optimizing the performance of the integrated system. This control can be exercised

directly by a utility if it owns all of the storage and generating equipment in a system,

but it can be exercised indirectly by such approaches as time-of-day pricing. For example, with time-of-day pricing, the costs of

nonoptimum performance of equipment not

owned by the utiIity wouId be communicated to the owners of this equipment

through higher prices for energy consumed

for backup power and lower rates for any

energy sold to the utiIity. The electric rates

now in effect in most parts of the United

States, however, do not have the effect of

enforcing optimum al locations between onsite and centralized generating equipment.

I n fact, many of the current rates tend to discourage onsite generation in spite of potential cost savings. (This problem is treated in

chapter VI Legal and Regulatory Issues. )

Figure V-1 illustrates the dramatic change

in electricity consumption in Great Britain

which occurred after a time-of-day electric

‘ ‘The Dow Chernlcal (lompdny, et al , Energy /ndustr/a/ Center Study. NSF Grant #OE P 7+2042, June

1975, p 70

rate was imposed. Before the rate was introduced, very little electricity was consumed during the night and an enormous

Figure V-1 .— Improvement in the Pattern of

Electricity Consumption in England’s South

Western Electricity Board Resulting From a

Shift to Time-of-Day Electricity Rates

in-

--- 1972/73 CONSTANT DAILY LOAD

LINE

O 3 6 9 12 15 18 21 24

HOURS

Winter-average Weekday Load Curve

SOURCE

Ash bury, J G and A. Kouvalls, E/ectrlc Storage Heaflng The Experience in Eng/and and Wa/es and Jn fhe Federa/ Repub/lc of

Gemrdr?y Arqonne Nallonal Laboratory, Energy and En

\ fro n men ta( Systpms DIVIS ron A N LJES 50 1976 P 14
Ch. V The Relationship Between Onsite Generation and Conventional Public Utilities . 147

crease occurred in the morning when electric heaters and other equipment were

turned on. After the variable rate was introduced, many consumers purchased onsite

thermal storage devices which could be

charged during the night and used to heat

buildings during the day. The result was a

much more uniform pattern of energy consumption.

STORAGE STRATEGY

Onsite solar electric devices integrated into electric utility grids provide a good example of some of the difficulties which can

arise from local control over storage equipment, A solar electric system which is not

connected to a utility grid would charge its

batteries during the day and discharge its

batteries during the night. This is precisely

the wrong strategy of operation from the

perspective of the electric utility since storage devices owned by the utility would be

charged during the night, when demands are

low, and discharged during the day when demands are greatest.

There will be some overlap between the

two operating strategies since both types of

storage wouId be discharging near sunset

and during cloudy days, but it is clear that

the storage equipment would be used to

best effect if it were controlled by the utility. The advantage of using the solar electric

devices to meet utility electric demands directly during the day (instead of sending it to

be stored) is arnplified by the fact that storage devices are typically only about 75-percent efficient This logic would apply even if

a very large fraction of the utility’s energy

were derived from solar sources, although in

this case the strategy of operating individual

storage systems would closely parallel the

operation of utiIity storage. (A quantitative

evaIuation of this issue appears i n the finaI

section of this chapter, )

LOAD MANAGEMENT

The performance of isolated and interconnected energy systems can be improved

if control is exercised over devices which

consume energy as well as over energy storage and generating equipment. Clearly, energy consumers will want to exercise as

much discretion as possible over the amount

of energy they use and when they use the

energy, but they also may be willing to

change their consuming habits to some extent if they are required to pay large premiums for energy consumed during periods

when energy is relatively expensive to produce. Consumers may be willing to postpone or defer the use of appliances such as

dishwashers, disposals, clothes washers and

dryers, and other equipment when electricity is expensive.

The utility can exercise control through

the use of “interruptible service” equipment

when onsite equipment includes onsite storage, Such devices wouId permit the utiIity to

turn off water heaters and other appliances

with storage capabilities during periods of

peak demand. Equipment of this type has

been installed for relatively large-scale testing by the Detroit Edison Co. If this equipment could ensure that onsite generating

equipment (whether thermal or electric) purchases backup power only during off peak

periods, the cost of backup energy to the onsite customer might be reduced — perhaps to

the point where energy could be bought and

sold at the same rate. An experiment was recently conducted in Vermont in which these

appliances were automatically turned off

when utility rates were high. The customers

were able to switch them back on again, but

in most cases were wilIing to wait untiI rates

fell.

24 Well-insulated water heaters and

freezers are able to operate effectively even

if their supplies of electricity are automatically shut off during the day when electricity prices are high. Several cities in Germany

have utilities which are able to exercise

elaborate control over energy-consuming

equipment The central load-management

“J G Ashbury and A Kouvalls, E/ectr/c Storag e

Heating The Experience in Eng/and and \l’a/es and In

the Federal ~epub/Jc of Cermany, Argonne Ndtlona i

Laboratory, Energy and Environmental Systems DIv I-

$Ion, ANL F S-50, 1976, p 20
148 ● Solar Technology to Today’s Energy Needs

computer can control both the generating

equipment and electricity-consuming d e -

vices. The computer sends a signal down the

electric wires which automatically shuts off

industrial equipment, refrigerators, water

heaters, and other equipment where energy

use can be deferred during peak periods. 25

As was the case with the control over

storage, however, the strategy of deferring

demand for energy will depend strongly on

how the solar devices are connected with

other energy equipment. If the solar device

operates in isolation, an attempt should be

made to shift all demands for energy to

periods when the sun is shining, If an electric utility is used for backup power, however, it will usually be preferable to shift the

demands which would require backup power to the late evening.

OFFPEAK ELECTRICITY

It is sometimes argued that electric utilities will be able to sell “off peak” electricity

at a rate which covers only the cost of operating a large “baseload” plant and the relatively inexpensive fuels which can be used

in these plants. Such rates are possible, but

they must be considered promotional since,

in effect, they subsidize the price of electricity during the night by charging daytime

customers for all other utility costs. These

costs are capital charges on generating

plants and transmission and distribution systems, the costs of maintaining the transmission and distribution lines, and all other

overhead costs — including the added cost

of maintaining dual meters for daytime and

nighttime rates.

It is also important to recognize that there

is not an unlimited supply of “off peak”

power available in a given utility. There are

many possible uses for the power available

at night, in addition to storing heat for

buildings. The power can be used to charge

batteries for electric vehicles and in other industrial procedures which can be deferred

to use night rates. The utilities may find that

they require the “off peak” nighttime energy

themselves to charge their own storage devices, if utiIity storage must be used as a replacement for the oil- and gas-fired generators now used to meet utility peaks. (The

National Energy Plan places major emphasis

on eliminating utility use of oil and gas. )

And utilities must also make some use of

off peak periods to maintain their equipment.

OWNERSHIP

The complex rates required to encourage

design of onsite equipment best suited for

the energy network of which it is a part,

would, of course, be obviated if utilities

owned the onsite systems outright. While

there clearly are disadvantages associated

with expanding the monopoly position of

utilities, there are a number of reasons for

believing that utility ownership of onsite

solar equipment may be attractive in many

circumstances:

● UtiIities are uniquely able to optimize

the mix of generating and storage

equipment in their service area and to

develop control strategies for minimiz-

“J [; Ashbury, op [-It , p 20

ing overall utility costs. (This could, of

course, also be done by a company

owning only transmission and distribution equipment, )

Utilities compare the cost of energy

derived from new solar equipment to

the cost of generating energy from new

electric-generating equipment or the

marginal cost of gas from new sources,

while all other solar owners must compare solar costs to the lower imbedded

costs of energy which determine commercial rates.

Utilities are probably better able to

raise large amounts of capital for long-
Ch. V The Relationship Between Onsite Generation and Convention/ Public Uti/ities ● 149

term energy investments than any other

type of organization. As the statistics in

table V-4 indicate, electric utilities require several times more capital per

dollar of sales than typical industrial

firms (although the capital intensity has

declined rapidly in recent years because of the rapid increase in fuel

costs) At the end of 1974, electric utilities owned approximately $150 billion

in plants and equipment— nearly 20

percent of all business plant equipment

in the United States.26

Table V-4. —The Capital Intensity of Major U.S.

Industries

[Dollars of plant to secure $1.00 of revenue]

$

Investor-owned electric companies:

(1965) . ., . . ., . ., ... ., .. .4.51

(1970) ., ., ., . . ., ., ., ... ., .. .,4.39

(1975) ., ., ., ., ., ., ... . . . . .3.20

(1977) (est. ) . , ., . . . 2.96

Bell Telephone System (1971 ) . ., . . . .. ..2.95

10 major railroads (1971) ., . ., ... ... .. .,2.48

Gas transmission companies (1971 ) . . . . . .2.43

Gas distribution companies (1971 ) . . . . . . .. .1.62

10 major integrated oil companies (1971) ., .. ..,1.25

500 diversified industrial companies (1971) .. ...0.87

50 major retailers (1971) . . . . . . . . . .. ..0.43

SOURCES Naf~ona/ Gas Survey U S Federal Power Commjsslon

Ebasco Services Incorporated (New York, N Y ), 1977

Bus{ness and Economic Charts p 28

An ability to raise capital for longterm investments is particularly critical

for solar energy devices since solar energy is very capital-intensive and typicalIy requires a number of years to return the initial investment. Utilities,

therefore, may be uniquely able to provide initial capital for solar devices in

situations where individuals (particularly individuals in lower income groups)

and organizations may find the capital

requirements prohibitive. Reverses in

the stock market, uncertainties about

“Federal Power Comm[ss[on, National Power Survey, Flnanc/ai Outlook for the Electric Power Industry.

Report and Recommendations of the Technical Advisory Comm/ttee on Finance, December 1974, P 50

the future of the energy industry, and

difficulties in obtaining rate changes

from utility commissions have, however, made it progressively more difficult for utilities to raise capital in recent years,

Utility capital tends to be less expensive than capital required by more speculative industries. A typical utility can

raise 50 percent of its capital from

debt–while most manufacturers rely

on debt for only 10 to 15 percent of new

investment capital, the remainder of

the capital being purchased at higher

rates from investors, 27 Utility capital

costs may, however, be higher than

those experienced by homeowners and

can be higher than the cost of capital

available for financing typical residential and commercial buildings. A home

owner earning a tax-free return of 10

percent on capital invested in solar

energy equipment may be well satisfied. This advantage is moot, of course,

if the individual is unable to raise any

capital for the project at al 1.

Utilities are already in the business of

selling energy and have the required infrastructure for billing, marketing, and

repairing equipment, Some potential

owners of onsite devices have been

wary of investing in equiprnent which

might lead them to unfamiIiar maintenance problems or the hiring of specialized personnel,

Utility ownership or marketing of solar

equipment and a willingness to stand

behind the equipment once installed

could increase consumer confidence in

the equipment.

There is some ambiguity, however, about

whether utility ownership of smalI solar energy equipment would be permitted by Federal antitrust statutes. The legal issues of

“Paul j Garfield and W F LoveJoy, Public Utility

Economics, Prentice Hall, Inc , Englewood Cllffs, N J ,

1964, p 25
150 ● Solar Technology to Today’s Energy Needs

ownership are discussed in greater detail in

chapter V 1, Legal and Regulatory Issues.

UTILITY ATTITUDES

There is no industrywide position either

on the issue of onsite generation or on the

question of utility ownership of such facilities, Industry attitudes vary company by

company, and the diversity of attitudes is

due, at least in part, to the fact that many

utility companies simply have not taken a

close look at the issue.

Natural gas utilities have expressed the

greatest recent interest in onsite solar facilities since supplies of gas are diminishing

and the companies are looking for new energy sources to replace natural gas in the

future. Southern California Gas Co., for example, has tested solar-assisted gas heating

for apartment buildings as one means of

conserving supplies and extending the Iife of

the company’s resources .28 Interest is not

confined to gas companies. A recent survey

found nearly 100 electric utilities which

were initiating projects in solar heating and

cooling.

29 30 The EIectric Power Research Institute has an extensive program in solar

energy equipment.31 At least one electric

utility has entered into an agreement with a

local installer of solar hot water heaters, and

a gas utility has proposed changes in regulations that would permit it to operate as a

combined gas and solar utility.32 33

‘aAlan Hlrshberg, Pub//c Po/icy for So/ar Heatin g

and Cooling, October 1976, p 37

“Solar Energy Intelligence Report, Feb. 14, 1977, p

31

‘“E Iectrlc Power Research Institute, Survey of E/ectric Utility So/ar Prolects, Palo Alto, Callf , ER 321 -SR,

1977

J‘ E Iectrlc Power Research I nstltute, E/ectric Power

Research Institute: So/ar Energy Program, fall of 1976,

E PRI RP 549, 1976

“E S Davis, Comrnercia/izing Solar Energy: The

Case for Gas Uti//ty Ownership, mlmeo, Jet Propulsion

Laboratory report, California Institute of Technology,

June 1976

“General Electrlc Corporation, conceptual design

study.

On the other hand, most of the utility

companies surveyed for a General EIectric

study referred to earlier said they were reluctant to enter the business of selling thermal energy systems. Some indicated that it

would require too much diversification;

others cited problems with metering and

other technical difficuIties.

A study conducted for the Federal Energy

Administration found mixed opinions

among utilities on expanding capacity by

using conventional onsite generating equipment, primarily cogeneration systems in factories and other generators of process

heat. Examples include:

●

●

●

●

A west-south-central utility which sells

both steam and electricity.

A Pacific coast utility, which has installed turbines at a paper mill, returns

low-temperature steam to the mill and

pays $0,01 per kWh for the electricity

generated.

A Vermont utility actively searching for

cogeneration opportunities.

A Texas utility which stated flatly that

they were “not in the business of selling

steam, ” and which turned down several

opportunities.

Although utility attitudes may be changing, there have been scattered complaints

that utilities have tried to thwart private

companies intending to instalI onsite generating equipment. The Dow Chemical Co. reports that onsite industrial cogeneration

“has been consistently discouraged by longstanding policies on the part of most privately owned electric utilities that have discouraged in every way possible the generation of electricity by any other type of organization. Relevant here are rate schedules

34 Dow Chemical Co , et al , Energy /ndustria/ Center

Study, June 1975, p 23

jSThermo E Iectron Corp., A Study of /rip/ant ~lectr;c

Power Generation in the Chernica/, Petro/eum Refining, and Paper and Pti/p /ndustries, June 1976
Ch. V The Relationship Between Onslte Generation and Conventional Public Utilities . 151

that favor large industrial users (whether if no power is used) that make it uneconomljustified or not by “cost of service”), and cal to use the utility as a standby source

heavy demand charges (charges levied even backing up industrial power generation “‘b

THE COST OF PROVIDING BACKUP

POWER FROM AN ELECTRIC UTILITY

There is no easy way to compute the cost

of providing backup power to an onsite system from a conventional electric utility

since electric utility costs are very sensitive

to the cost of equipment and fuels in the

area being served and to the times when

electric backup power is demanded. A simple technique for computing these costs is

presented here to illustrate some of the major trends, to exhibit several different ways

of looking at the major trends, and to exhibit

several different ways of looking at the issue

of rates. It must be emphasized from the onset that the method cannot be taken to be a

precise calculation of the costs of electric

utiIities actualIy operating in the regions

covered. The results are so sensitive to local

conditions that each utiIity must make its

own analysis of the costs. The following

analysis shows that utiIity costs are extreme

Iy sensitive to four variables:

● The regional cost of equipment, the

available financing, and the local cost

of fuels;

● Local climatic conditions [for example,

solar backup costs are lower if peak

heating and cooling periods are correlated with periods of clear skies);

● The type of solar equipment installed

(collector area, storage capacity, etc.);

and

Ž The number of buiIdings in a utiIity

service area equipped with solar energy

devices (a relatively small number of

solar facilities will contribute to load

diversity, but a large number will reverse this resuIt).

The details of the technique used to compute utility costs, and detailed assumptions

made about the costs of equipment and

fuels experienced by each utlIity, are described in detail in appendix A of this

chapter, but the basic method IS straightforward:

1 .

2

3

A “baseline” utility was constructed by

combining the electric demands of a

number of buildings and industrial

processes using a mixture of energyconsuming equipment which was typical for the city under examination. The

cost of providing electricity for the

combined utility load was then computed, assuming that the utility was optimized to meet the demands. (Both the

cost of energy attributable only to the

generating units, the so-called “busbar

costs, ” and the cost of energy delivered

to customers were computed).

The cost of meeting a new set of electric demands resulting from adding a

specified number of solar and nonsolar

buildings to the utility was computed,

assuming that the utility was optimized

to meet the new demand pattern.

The effective cost of providing backup

power for different types of buildings

could then be computed by examining

the incremental costs and the incremental utility costs which resulted

when the new buiIdings were added,

Since it was assumed that all of the equipment in the utility was new, and the costs

computed are all essentialIy marginal costs,

the actual utility costs in the region would

be lower because some fraction of the ener-

“ DOW Chemical Co , et al , Energy /ndustr/a/ Center

Study, June 1975, p 23
152 Ž Solar Technology to Today’s Energy Needs

gy would be generated from less-expensive,

older plants. There are a number of other artificial ities in the technique:

●

●

●

The choice of an “optimum” set of utility equipment does not use a detailed

analysis of overall system reliability

and maintenance schedules— it instead

simply assumes that the utility will purchase 20 percent more in each generating capacity than the peak required in ,

that category to meet the load;

Utilities will seldom be able to deploy

equipment which is optimally suited to

load patterns because of regulatory delays, an inability to precisely predict demands, and the need to use older equipment; and

I t was assumed that none of the utilities

evaluated owned storage equipment. In

the future, utility storage devices may

play a major role in replacing the oiland gas-burning devices now used to

meet real demands. The impact of storage on the cost of backup power for

solar systems will need to be carefully

examined. One would expect that lowcost storage would minimize the negative impacts of solar equipment.

This technique has been used to compute

the cost of providing electric power to a

number of different single family houses,

and the results are summarized in table V-5.

This table compares the cost per kWh of

providing electricity to the building described to the cost per kWh of providing

electricity to a similar building using an

electric heat pump. AlI comparisons are between delivered costs. Greater detail on the

utility costs and the capacity of equipment

installed is presented in volume I I.) For example, the table indicates that the electricity required by a single family house using

gas for heating, water heating, and airconditioning in Albuquerque, N. Mex., costs

the utility 2 percent more than the electricity used to provide power for a conventional

single family house in the same city using a

heat pump and electric hot water.

An examination of table V-5 reveals several

Ž

●

●

●

features:

Electricity for conventional houses using gas for everything other than fans

and miscellaneous electric loads costs

the utility approximately the same

amount as electricity for a heat-pump

house.

Electricity costs are lower for houses

using electric resistance heat (presumably because they use more electricity

during periods of mild winter weather

when utility demands are relatively

low) and are higher for houses using gas

heat and electric air-conditioning. (All

of the utilities examined have peaks in

the summer, and these peaks are increased by the added air-conditioning.

But the added equipment is underutilized since the new houses do not use

much electricity during the winter. )

The houses using solar energy for heating and hot water and a heat-pump

backup cost the utility more per kWh

than the conventional houses using

baseboard heat, but less than the

houses using gas heat.

The photovoltaic houses cost some

what more than the houses equipped

only with solar heating and hot water,

but in no case is the utility cost significantly larger than the cost of providing backup power for a heat-pump

house– in several instances, the utility

costs are lower in the solar cases. The

relatively favorable appearance of

these solar systems results in part from

the fact that some of the utility air-conditioning peaks can be reduced by the

solar devices. (About 50 percent of the

total building energy requirement is

provided by the photovoltaic devices,

and about 30 percent of the total energy requirement of the house is provided

by the heating and hot water systems.)

Utility costs per kWh of backup power

delivered are increased slightly if sales

to the utility are permitted.
Ch. V The Relationship Between Onsite Generation and Convention/ Public Utilities ● 1 5 3

Table V-5.—The Fractional Difference Between the Utility Costs [¢/kWh] Required to Provide Backup

Power to the Systems Shown and the Costs to Provide Power to a Residence Equipped With an

Electric Heat Pump [see note for explanation]

1.

2

3.

4.

5.

Albuquerque Boston Fort Worth Omaha

Single family house with gas heat,

hot water, and alr-conditioning” . . 0.02 -0.09 -0.15 0.03

Single family house with gas heat

and hot water, and central electric air-conditioning ● . . . . . . . . . . . 0.26 0.28 0.15 0.32

Single family house with baseboard heat, electric hot water, and

window air-conditioning” . . . . . . – 0.14 -0.14 -0.15 -0.10

Single family house with solar heat

and hot water backed up with a

heat pump and electric hot water* 0.01 -0.13 0.06 -0.07

Single family house with extra insulation, electric hot water, and

heat pump with: ● ●

a. Photovoltaic system with no

battery and no sale to the utility . . . . . . . . . . . . . . . . . . . . . . . . -0.06 -0.27 ‘0.02 -0.07

b. Photovoltaic system with no

battery and sales to utility permitted, . . . . . . . . . . . . . . . . . . . . 0.07 -0.23 0.03 -0.01

C. Photovoltaic system with battery and no sales to utility. . . . . -0.30 -0.27 0.01 -0.05

“ Compared with single family house with electric hot water and heat Pump.

“’ Compared with single family house with extra insulation, electrlc not water, and heat pump,

NOTE: let Cr = Incremental utlllty costs resulting from adding 1,000 reference houses with heat pumps.

let Kr = the Incremental number of kWh generated when 1,000 reference houses with heat pumps are added to the utility

let Ct and Kt be the equivalent quantities resulting from adding 1,000 houses with a different kind of energy equi Prnent

Then the fractional change JJlustrated above Is given as follows: F = Ct/Kt - Cr/Kr

Cr/Kr

Table V-6 indicates the Ievelized monthly

costs which would be experienced by consumers if they were charged electric rates

reflecting the marginal cost of providing

energy to several types of energy systems.

Levelized costs assuming a moderate rate of

increase in electric prices are shown f o r

comparison. In these cases, it is assumed

that an electric utility will purchase electricity from the onsite generating facility for

50 percent of the price at which it sells electricity. (In the cases when the electric price

28-842 () - 11

was assumed to be the marginal cost of providing backup — giving credit to the value of

electricity sold to the utility— it was assumed that electricity is bought and sold at

the same price. )

Except for Boston, the two techniques for

computing Ievelized energy costs produce

similar estimates of Ievelized energy

charges. (It is Iikely that the techniques used

to compute the marginal costs of electricity

are overly optimistic about the costs of new
154 Ž Solar Technology to Today’s Energy Needs

Table V-6.—Levelized Monthly Costs for a Well-Insulated Single Family House Showing the Effect

of Marginal Costing for Backup Power

I. ALBUQUERQUE

—no solar. . . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, no sales to the

the utility . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

Il. BOSTON

—no solar. . . . . . . . . . . . . . . , . . .

—59 m2 silicon photovoltaics,

no batteries, no sales to the

Utility . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted ., . . . . . . . . . . . . . . . .

Ill. FORT WORTH

—no solar. . . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, no sales to the

utility . . . . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

IV. OMAHA

—no solar. . . . . . . . . . . . , . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, no sales to the

utility . . . . . . . . . . . . . . . ., . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

—59 m2 silicon photovoltaics,

no batteries, sales to utility

permitted . . . . . . . . . . . . . . . . . .

Electricity rates assumed to Electricity rates reflect marginal

increase by BNL forecast utility rates

(see appendix for methodology)

No credits 20% ITC on No credits 20% ITC on

given solar equipment given solar equipment

183

213(255)

197(240)

216(267)

300

319(362)

305(348)

324(376)

190

228(272)

218(263)

240(293)

211

241 (284)

231 (275)

253(305)

183

202(246)

187(231 )

204(257)

300

308(353)

294(339)

311 (365)

190

216(262)

207(253)

226(281 )

211

230(275)

220(265)

239(294)

204

21 4(257)

190(232)

194(245)

215

215(259)

200(244)

227(279)

191

227(272)

212(257)

242(295)

219

238(282)

223(267)

250(303)

204

204(248)

179(223)

181 (234)

215

204(249)

189(234)

21 3(267)

191

216(262)

201 (247)

228(283)

219

228(273

21 2(258

237(291 )

NOTES: (1) All houses use heat pumps for space conditioning and electric resistance hot water heaters

(2) Parenthesis ( ~ indicates utility ownership.

(3) ITC = Investment Tax Credit
Ch. V The Relationship Between Onsite Generation and Convention/ Public Uti/ities Ž 155

equipment in that region. ) More importantly, however, the ranking of the Ievelized

costs of the four systems appears not to depend on whether marginal costs or average

costs are used to make estimates.

The same methods can be used to estimate the price a utility should be able to

pay for electricity produced by an onsite

device which exceeds onsite demands. This

can be done simply by computing the difference in utility costs which results when a

group of solar buildings is permitted to sell

energy and dividing this cost by the total

amount of kWh sold. The results are presented in table V-7 as a ratio between the

value of the electricity available for purchase and the average cost of electricity

generated by the utility. Since all costs in

the utility used in this analysis are effectively “marginal costs,” the onsite devices are

Table V-7.—Ratio of Price Utilities Can Pay for Solar Energy Generated Onsite to the Price

Charged by Utilities for Electricity

Albuquerque Boston Fort Worth Omaha

Purchase Purchase Purchase Purchase Purchase Purchase Purchase Purchase

base reference base reference base reference base reference

1. Single family

house with no

onsite batteries . . . . . .

2. Single family

house with

onsite batteries . . . . . . .

3. Single family

house with

extra insulation and no

onsite batteries . . . . . . .

4. High rise

apartment with

no onsite batteries . . . . . . .

5. High rise

apartment with

onsite batteries . . . . . . .

0.67 0.65 0.62 0.55 0.31 0.28 0.57 0.59

0.40 0.39 1.09 0.98 0.29 0.26 0.64 0.66

0.64 0.62 0.58 0.49 0.66 0.64 0.50 0.50

0.64 0.66 0.51 0.48 0.29 0.29 0.42 0.44

0.41 0.43 0.38 0.36 0.29 0.28 0.36 0.38

Let x n (utlllty cost supplylng buildlng not selling electricity minus utility costs for building selling excess electricity to the utility)

Let y = (kWh generated by utility In supplying buildlng not selling electricity minus utility costs in supplying building selling excess

electrlclty)

Let z n (added utility cost incurred in supplying building with no solar equipment) divided

the bulldlng)

Let w = (total utlllty costs) dlvlded by (total kWh produced by the utility)—no additional buildings

Purchase = Xly Purchase = Xly

Base w Reference x

All utlltty costs are dellvered costs

by (added kWh required to supply
156 . Solar Technology to Today’s Energy Needs

not given credit for the difference between

the imbedded average utility costs used to

determine selling prices and the fact that

new solar systems will displace relatively expensive “new” generating facilities.

Table V-8 shows information for high rise

apartment buildings which is equivalent to

the data for single family houses shown in

table V-7. It can be seen that the solar devices are less attractive to the utility in these

cases, in part because the reference case

chosen for the high rise building uses electric baseboard heating—which produces a

more even load than the heat pumps used

for the single family reference case.

As noted earlier in this chapter, the costs

of providing electricity can be reduced if onsite storage is available at each building site

which permits the buiIding to purchase energy during periods when the demand on the

utility is relatively low. Solar equipment, of

course, is typically already equipped with a

thermal storage device, and these devices

can be converted to allow the system to purchase energy only during off peak periods

with a relatively simple change in their control systems. The result of installing off peak

storage devices in a number of different

types of buildings is shown in tables V-9 and

V-10. Chilled water can also be produced

during the night and stored in tanks to

reduce cooling loads during the day. The use

of “off peak cooling” has the additional advantage of allowing the chilling equipment

to operate at night when it is more efficient.

In computing the load pattern, it was assumed that the storage devices are charged

between midnight and 5 a.m. and that the

amount stored is equal to the amount of

backup energy for heating, hot water, and

cooling which would have been required for

the previous day with no off peak storage.

An examination of tables V-9 and V-10

shows that the savings to the utility can be

considerable if off peak storage is used onsite. In the case of off peak storage of cooling, utility costs per kWh attributable to the

house are reduced by nearly 50 percent. In

all cases, the reduction in costs is lower if

solar equipment is installed, but in many instances the difference is not very large. Typically, the utility cost per kWh to provide

backup power for the solar houses with offpeak storage is about 10 percent greater

Table V-8.—The Fractional Difference Between the Utility Costs Required To Provide Backup

to the Systems Shown and the Costs of Providing Power to a High Rise Apartment

Equipped With Central Electric Air-Conditioning, Electric Hot Water, and Baseboard Resistance Heating

[see notes on previous table for explanation of how these fractional changes are computed]

Building equipment Albuquerque Boston Fort Worth Omaha

1.

2.

3.

Gas heat, gas hot water, and gas

air-conditioning. . . . . . . . . . . . . . . . . . . . . . . . . . 0 -0.11 -0.12 -0.05

Gas heat, gas hot water, electric airconditioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 0.32 0.21 0.26

Electric hot water, electric baseboard

heat, central electric air-conditioning, and

a photovoltaic system:

a. No batteries onsite, no sales to grid . . . . . 0.27 -0.01 0.21 0.03

b. No batteries onsite, sales to grid allowed . 0.31 -0.02 0.23 0.09

c. Batteries onsite, no sales to grid . . . . . . . . 0.28 -0.02 0.22 0.08

d. Batteries used onsite, sales to grid

allowed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31 -0.02 0.22 0.08
Ch. V The Relationship Between Onsite Generation and Conventional Public Utilities ● 157

Table V-9.—The Impact of Off peak Storage on Utility Costs

[fractional increase or decrease in backup costs per kWh–see notes]

Albuquerqu e Boston Fort Worth Omah a

Nonsolar houses

● Off peak storage for heat and hot water . . . . . . . -0.37 -0.38 -0.29 -0.34

● Off peak storage for heat, hot water, and

cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.47 -0.45 -0.48 -0.44

Houses with solar heating and hot water

. No off peak storage . . . . . . . . . . . . . . . . . . . 0.03 -0.11 0.12 -0.06

Ž Off peak storage for heating and hot water . . . -0.11 -0.24 0.003 -0.21

. Off peak storage of heating, hot water, and

cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.30 -0.35 -0.32 -0.36

Notes The t‘ reference house’ is a single family house using electric resistance heating and hot water and window air-conditioners

All solar houses generate only heating and hot water from solar energy.

Let Cr = added u tI I It y costs resu It I ng from the add It ton of 1,000 reference houses

K r = added kWh resu It I ng from the add It Ion of 1,000 reference houses

% =

added u tI I Ity costs resu It Ing from the addlt Ion of 1,000 test houses (type noted In left column above)

K =

added u tI I Ity costs resu It I ng from the add!t Ion of 1,000 test houses

The fractional change ratto shown above IS calculated as follows:

(Ct/Kt) - (Cr/Kr)

F=

(Cr/Kr)

than the utility cost per kWh attributable to

conventional houses with off peak storage.

It is apparent that the solar systems have

more difficulty competing with conventional electric heating systems if the conventional devices use off peak storage and are

able to buy electricity during off peak periods at reduced rates. There are, however,

still a number of cases in the examples

shown where solar devices are able to compete. Off peak storage equipment, while not

as expensive as solar devices, can still be

costly: they require the installation of heating (or chilIing) equipment which is larger in

capacity than conventional equipment by

the ratio of 24 hours to the number of hours

used to charge storage; with existing technology, heat pumps cannot be used to

charge off peak heat storage and resistance

heating must be used; and the devices require more sophisticated controls than ordinary heating systems. Another difficulty

with storage of off peak electricity in the

form of thermal energy to be used for space

heating is that, in the climates examined in

this study, the use of off peak storage Ied to

a significant increase in the electricity consumed by each building—which would reduce the economic advantage to the building owner of using off peak storage. It must

also be recognized that the costs shown in

the tables implicity assume that an ideal

“marginal rate” is charged in which the utility is able to charge each customer precisely

the real incremental cost incurred by the

utility in supplying that customer. In this

sense, the costs represent a “best case” for

off peak power. The rates also do not include additional charges which might result

from additional metering and bilIing. The results may indicate, however, that in the

long-run conventional electric utilities may

prove to be poor choices for providing backup power to onsite solar instalIations.
158 Ž Solar Technology to Today’s Energy Needs

Table V-10.—Levelized Monthly Costs for a Single Family House Showing the Effect of Marginal

Costing and Buying of Off peak Power

Electricity rates assumed Electricity rates reflect

to increase by BNL forecast marginal utility rates

(see appendix for methodology)

200% ITC on 20% ITC on

No solar & off peak No solar & off peak

credits equipment credits equipment

i. Albuquerque

—No solar or off peak buying:

. Electric resistance heat. . . .

● Heat pump heat . . . . . . . . . .

—Solar only:

● Low cost coils . . , . . . . . . .

Ž High cost . . . . . . . . .

—Offpeak heating, & hot water

only . . . . . . . . . . . . . . . . . . . . . .

—Offpeak heating, cooling &

hot water only. . . . . . . . . . . . . .

—Solar & off peak heating & hot

water

● Low Cost coils . . . . . . . . . .

● High cost coils . . . . . . . . . .

—Solar & off peak heating, cooling & hot water

● Low Cost coils . . . . . . . . . . .

● High cost CO iIS. . . . . . . . . . .

Il. Omaha

—No solar or off peak buying:

● Electric resistance heat. . . .

● Heat pump heat . . . . . . . . . .

—Solar only

● Low Cost coils . . . . . . . . . .

Ž High cost COiIS . . . . . . . . . . .

—Offpeak heating & hot water

only . . . . . . . . . . . . . . . . . . . . . .

—Offpeak heating, cooling &

hot water only. . . . . . . . . . . . . .

—Solar & off peak heating & hot

water

● Low COSt Coils . . . . . . . . . .

. High cost colts. . . . . . . . . . .

—Solar & off peak heating cooling & hot water

● Low Cost Coils . . . . . . . . . . .

Ž High cost coILs. . . . . . . . .

239

204

185(21 1 )

205(240)

N /A

N 1A

N /A

N /A

N /A

N/A

278

250

252(282)

278(320)

N/A

N/A

N/A

N/A

N/A

N/A

239

204

179(205)

196(232)

N / A

N /A

N /A

N /A

241

229

183(209)

203(238)

185(205)

198(232)

177(207)

197(236)

N/A 194(242)

N/A 214(272)

278

250

244(276)

267(31 1 )

N/A

N/A

N/A

N/A

N/A

N/A

278

268

234(265)

261 (303)

219(241 )

237(278)

221 (258)

247(296)

244(303)

270(341 )

241

229

177(203

194(230)

181 (201 )

189(225)

169(200)

186(227)

181 (231 )

198(258)

278

268

227(259)

250(294)

21 4(237)

227(270)

211 (250)

234(284)

228(289)

250(324)

NOTE: Solar systems are thermal only; Housea are SF-3
Ch. V The Relationship Between Onsite Generation and Convention/ Public Utilities Ž 159

Table V-1 O also shows that when contemporary rate schedules are used, it costs less

to heat a single family house with a heat

pump than with electric resistance baseboard heat. The difference in costs narrows

considerably, however, if marginal costs are

charged. The resistance system actually is

less expensive if off peak storage is used in

connection with the resistance heating. The

disadvantages of heat-pump systems would

be magnified if a large number of customers

in the regions examined used electric heatBACKUP POWER

ing and the utility peak occurred in the

winter (both utilities examined have summer

peaks). The heat-pump systems would be

more attractive, if their performance were

improved or a technique could be developed for storing off peak energy for use during periods when the heat-pump capacity is

inadequate to meet the load; in current systems, straight resistance heating is used in

such situations. Clearly, more analysis is required in this area.

WITH ENERGY

SOURCES OTHER THAN ELECTRICITY

It was noted earlier that the cost of providing backup for solar equipment from relatively expensive electric-generating equipment may be so great that it would be preferable to provide backup by using seasonal

storage systems or relying on gas I n fact, it

has been suggested that electric utilities,

with their high capital costs, are uniquely

unsuited to providing backup for solar

equipment. 37 Analysis presented in volume

II shows that for large buildings (and for

single famiIy structures which can pipe thermal energy to a central storage site), solar

heating and hot water systems capable of

providing 100 percent of local requirements

may become economicalIy competitive with

1‘J oseph C Ashbury and Ronald 0 A!LJel Ier, “solar

Energy and E Iectrlc Ut I I It le~ Shou Id They be Intertdceci?” \c/ence, 1954127, p 445 (1977]

electric heating and hot water in many parts

of the country in the relatively near future.

Table V-11 indicates some comparisons

between gas and electric backup. In the gas

cases, it is assumed that the system is not

connected to an electric grid. Backup is provided by a small, 32-percent efficient engine

burning natural gas to power a heat pump

Electricity for lighting and other uses is provided from a generator attached to the heatpump engine The table indicates that the

gas backup alternative may be attractive

even if gas prices increase drasticalIy over

the next few decades This possibility may

make it interesting to consider the possibility of granting preferential allocation of

gas to facilities using gas to backup solar facilities and permitting new gas hookups in

regions where such hookups are now permitted if the gas is used as a solar backup
760 ● Solar Technology to Today’s Energy Needs

Table V-n .—Levelized Monthly Costs of Several Kinds of Energy Equipment in a

Single Family Detached Residence in Albuquerque, N. Mex.

(dollars per month)

Gas price in 2000 (¢/kWh) . . . . . . 0.005 0.011 0.015 0.03

Electric price in 2000

(¢/kWh) . . . . . . . . . . . . . . . . . . . . . 3 4.5 10 —

Incentive ... , ., . . . . . . . . . . . . . . none

1.

2.

156

3.

4.

5.

6.

7.

Heat pump, electric hot

water . . . . . . . . . . . . . . . . . . . . . . .

Solar heat and hot water, electric

heat pump backup

—High. . . . . . . . . . . . . . . . . . . . . .

—Low . . . . . . . . . . . . . . . . . . . . . .

Extra insulation, 59 m2 photovoltaics at $500 kW, electric heat

pump backup

—No batteries . . . . . . . . . . . . . . .

—20 kWh batteries at

$70/kWh . . . . . . . . . . . . . . . . . . . .

Gas heat and hot water, central

electric air-conditioning , . . . . . .

Solar heat and hot water backup,

electric air-conditioning

—High. . . . . . . . . . . . . . . . . . . . . .

—Low . . . . . . . . . . . . . . . . . . . . . .

Extra insulation, 50 m

2

photovoltaics a t $500/kW,

gasfired heat pump/generator

backup. . . . . . . . . . . . . . . . . . . . . .

Solar heat with central seasonal

storage, homes connected with

hot water piping, electric airconditioning in each house

—High. . . . . . . . . . . . . . . . . . . . .

—Low . . . . . . . . . . . . . . . . . . . . . .

187(223)

158(1 83)

169(207)

190(228)

116

172(21 O)

1 43(1 70)

157(1 96)

21 4(292)

164(21 2)

none

203

213(250)

184(210)

196(233)

215(253)

173

201 (239)

172(1 99)

177(21 5)

233(31 1 )

184(231 )

20%

tax credit

395

309(354)

284(315)

294(338)

303(349)

287

276(323)

251 (284)

182(230)

290(383)

249(306)

20%

tax credit

—

—

—

—

—

500

422(469)

379(430)

203(277)

—

—

Percent of total

energy usage

supplied by

solar energy

o

28

28

52

45

0

41

41

50

65

65

Notes: All costs In 1976 dollars

( ) = utlllty ownership
Appendix V-A

Analytical Methods

Electric utility load pat

conveniently summarized

BACKGROUND

ems can be most

in what is known

as a “load-duration curve. ” The curve for a

hypothetical utility is shown in figure V-A-1.

It shows the number of hours per year the

demand for electricity is greater than or

equal to alI demands from zero to the annual peak For example, the figure shows

that the power company in question had a

maximum load of 100 MWe and a minimum

load of 25,0 MWe (i. e , the company produced at least 250 MWe for all 8,760 hours

of the year). The company met a load which

was greater than or equal to 50 MWe for at

least 3,504 hours during the year Loads will

increase with each new year as a result of

population growth and increases in the electricity consumed by each person. The increase in per capita consumption is a result

of a shift to electric heating and other electric appliances.

If solar equipment is installed in a significant fraction of the buildings served by a

utiIity, the load pattern which it must meet

could be significantly affected. Figure V-A-1

illustrates two extreme possibilities. We

assume that curve 1 indicates the load-duration curve which a utiIity could expect if

no solar equipment were installed. If solar

equipment requiring supplementary power

during a utility’s peak demand hours and

not during off peak hours was installed, a

load-duration curve having roughly th e

shape of curve 2 would resuIt.

The amount of electricity sold would

sequently be reduced, but costs would

 con-

 no t

be reduced proportionately because a large

fraction of utility costs are independent of

the amount of electricity generated. In this

case, a utility will have proportionately

more peaking plants with relatively small

capital costs, Unfortunately, such plants are

less efficient than large plants in both their

fuel consumption and operating and maintenance expenses. Curve 3 indicates a situation where the solar equipment installed

does not require supplementary power during the utiIity’s peak demand hours, I n this

case, more efficient generating facilities

(baseload plants and cycling plants) would

be used to produce a greater fraction of the

total utility load, resulting in a lower cost for

each kiIowatt-hour generated.

In order to quantify both the extent of the

impact and whether it is adverse or beneficial, it is necessary to construct a “typical”

utiIity. From this, several Ioad-duration

curves for the utility’s operation can be constructed for 1985, involving a variety of

scenarios both with and without solar equipment. These hypothetical load-duration

curves can then be used to determine the

kinds of equipment utilities will have to instalI to meet the demand of their customers,

and the Ioadfactors for each piece of generating equipment. In turn, electricity costs

and the utility’s fossil-fuel requirements can

be estimated for each scenario,

CHARACTERISTICS OF A “TYPICAL” UTILITY

The model utility examined is as close as

possible to a “typical” utility which matches

the national average for privately owne d

electric utilities wherever possible. The following sections briefly outline the physical

and financial structure of the utility at the

end of 1975.
162 ● Solar Technology to Today’s Energy Needs

Figure V-A-1 .—A Typical Load-Duration Curve for an Electric Utility

Curve #1 — —

Curve #2 — — — –

Curve #3 - — - —

I I I I I I I I

20 40 60 80 100

(1 752) (3504) (5256) (7058) (8760)

Percent of time indicated load is exceeded

(Hours)

Source: OTA.
Appendix V-A

CHARACTER

MODEL

The hourly loads

ISTICS OF THE

UTILITIES

used to evaluate the

cost of generation are constructed by combining the hourly electrical loads which

apply to individual buiIding types The

method for determining the hourly electric

demands of individual buildings is explalned

in Volume I I, The number of customers i n a

typical private U. S. utility IS shown in table

V-A-I. The number of buildings of each type

used to construct the model utility used

here for analysis is shown in table V-A-2.

Table V-A-1 .—Average Characteristics of

Table V-A-2.—Numbers of Buildings in “Typical” Utility Modeled Which Use

Heating and Cooling and Hot Water Equipment*

— . . — .———— ———.

Albuquerque Boston Fort Worth Omaha

Single family detached houses

Baseboard resistance heating. . . . . . . . . . . . . .

Central electric air-conditioning . . . . . . . . . . . .

Window air-conditioning . . . . . . . . . . . . . . . . . .

Electric hot water . . . . . . . . . . . . . . . . . . . . . . . .

Total single family houses. . . . . . . . . . . . . . . . .

Townhouses

Baseboard resistance heating. . . . . . . . . . . . . .

Central electric air-conditioning . . . . . . . . . . . .

Window air-conditioning . . . . . . . . . . . . . . . . . .

Electric hot water . . . . . . . . . . . . . . . . . . . . . . . .

Total townhouses . . . . . . . . . . . . . . . . . . . . . . . .

Low rise apartments

Baseboard resistance heating. . . . . . . . . . . . . .

Central electric air-conditioning . . . . . . . . . . . .

Window air-conditioning . . . . . . . . . . . . . . . . . .

Electric hot water . . . . . . . . . . . . . . . . . . . . . . . .

Total low rise apartments. . . . . . . . . . . . . . . . . .

High rise apartments

Fancoil resistance heating . . . . . . . . . . . . . . . .

Baseboard electric heating . . . . . . . . . . . . . . . .

Central electric chiller . . . . . . . . . . . . . . . . . . . .

Window air-conditioning . . . . . . . . . . . . . . . . . .

Electric hot water . . . . . . . . . . . . . . . . . . . . . . . .

Total high rise apartments. . . . . . . . . . . . . . . .

Shopping centers

Central electric chiller . . . . . . . . . . . . . . . . . . . .

Electric resistance heating . . . . . . . . . . . . . . . .

Total shopping centers. . . . . . . . . . . . . . . . . . . .

10,470

35,450

8,163

15,840

55,920

648

4,132

424

1,043

6,960

201

1,282

132

324

2,160

28

28

196

196

90

600

30

15

30

8,080

29,823

5,040

18,080

55,920

1,429

3,464

895

1,211

6,960

444

1,075

278

376

2,160

62

62

188

188

104

600

0

0

0

11,790

44,130

11,790

16,970

55,920

2,010

4,950

2,010

1,120

6,960

624

1,536

624

348

2,160

87

87

30

30

97

600

30

15

30

7,719

48,200

7,719

17,970

55,920

1,350

5,610

1,350

1,208

6,960

419

1,741

419

375

2,160

58

58

300

300

104

600

30

15

30

● All figures are number of buildings not units—the townhouses have 8 units each, the low rise apartments 36 units

each, and the high rise apartments 196 units each.

NOTE: Detailed assumptions about the buildings modeled can be found In volume 11, chapter I Ar?a/y?ica/ Methods.
164 ● Solar Technology to Today’s Energy Needs

Commercial demands are approximated

by simply using 30 shopping centers. A more

detailed model would require many more

load types–schools, hospitals, etc. industrial demand was approximated as a weekly

load which is not weather dependent. Hourly industrial loads used in the utility model

are shown in table V-A-3. They were chosen

after examining a number of actual utility

industrial loads. There are great variations in

these loads around the country, and the

data used can only show one “typical” pattern. Weekend loads were assumed to be 40

percent of the weekday loads. The total

yearly industrial load served by the utility is

2.532 X 1 0

9 kWh .

Table V-A”3.—lndustrial Load Profile Used

Hour Weekday Weekend

LOAD DIVERSITY

The load diversity factor used in forming

an aggregated utility load was determined

as follows:

1. It was assumed that heating and airconditioning loads had no diversity,

since all buildings in the area would be

2

affected by approximately the same

weather at approximately the same

time. (This is a conservative assumption. Most utilities cover areas sufficiently large enough to expect some

weather diversity. Tielines can be used

between widely spaced utilities to even

out weather loads. )

It was assumed that the hourly variation of “miscellaneous electric loads”

and domestic hot water loads was the

same for each building of a similar

type. When they were added, however,

it was assumed that each sequence

started at a different time. The spread

in “start times” was assumed to be the

spread during which people wake up in

the morning, eat, and go to work which,

in turn, was assumed to be the same as

the spread of traffic during rush-hour

peaks in major cities (i. e., a normal

distribution with a standard deviation

of approximately 1 hour).

This technique is expressed quantitatively

in the expression below:

0 0

where f(t) is the hourly load profiIe of an individual house, fN

(t) is the hourly load profile of an aggregate of N such individual

houses if N is large and if “wake-up times”

are distributed in a Gaussoan distribution

with a standard deviation of ó hours. The

results of this smoothing for a variety of different values of the standard deviation are

shown in figures V-A-2 and V-A-3.

SIZING GENERATING EQUIPMENT

The generating equipment installed by

the utility depends on the load-duration

curve (which characterizes customer demands), costs of purchasing and operating

alternative types of generating equipment,

kinds of financing available to the utility,
Appendix V-A ● 1 6 5

Figure V-A-2.— Ratio of Peak Demands to Average Demands as a Function of the

Standard Deviation of “Wake-Up” Times

4

3

2

1

Standard deviation of “wake-up” times (hours)

Source: OTA
166 . Solar Technology to Today’s Energy Needs

I I I
Appendix V-A ● 1 6 7

—

and current and projected fuel costs. As

selecting the best mix of generating equipment is a complex task, a greatly simplified

approximation of the techniques actually

employed by utiIIties IS used, The selection

of the appropriate mIX of such plants for

meeting any Ioad-duration curve is dominated by the fact that: (1 ) larger plants have

relatively high efficiencies and high initial

costs and, as a result, are profitable only if

operated for a large fraction of the year; and

(2) smaller gas turbines and internal combustion systems are relatively inexpensive to

purchase, but have relatively high-cost fuel

consumption and are thus best used in situations where they operate only a few hours

each day Larger plants, therefore, are used

to meet the “baseload” requirements of the

utility (the loads which will be constant

throughout the year), with the smalIer plants

used for intermediate and “peaking” purposes when the demand is greater than the

baseload plant capacity

Storage can be used to meet some demands during peak periods If the utility has

facilities for storing energy. Peaking plants

would then be used only when storage output capabiIities were exhausted

The heuristic arguments given above can

be quantified quite easily if a few simplifying approximations are made The basic

parameter used to evaluate a utility system

is the total “levelized” annual cost of producing electricity (which is called CT in the

following discussion). This cost is the sum of

the cost of capital invested in equipment

and the average annual fuel, operating, and

maintenance costs, Following the notation

developed in the discussion of economic

and financial analysis found in volume 11,

chapter 1, the Ievelized annual cost of a

piece of equipment is given as follows:

Cost = k1 x (Initial equipment cost)

+ k2 x (amount of fuel used annually) (2)

+ k3 x (annual operating cost)

Here k, is the effective cost of capital, k2 i s

a “levelized” fuel cost (which may differ

from current fuel costs because of projected

fuel price increases), and k3 is a multiplier

leveling the presumed inflation of operating

costs.

The annual cost of operating a given

piece of generating equipment can then be

written as follows:*

(4)

* Index
168 ● Solar Technology to Today’s Energy Needs

ward improvement to the current model

would be to assume that the operating costs

were of a form X + YT, but the current

method was chosen for simplicity. Another

approximation which has been made is that

the efficiency is independent of the operating strategy.

The utility’s total operating costs can then

be approximated by examining the load-duration curve. Figure V-A-4 (which is an inverted load-duration curve) illustrates the

sequence in which loads are met by generating plants. T(D) is the number of hours per

T . = 8760 hours

■

Figure V-A-4.— Inverted Load-Duration Curve of a Typical Electric Load

T(D)

Base load

Intermediate

Source: OTA. Demand (kW)
Appendix V-A ● 1 6 9

year when the utility’s load exceeds D kilowatts. When there is no storage, the approximate cost is given by:

The optimum set of equipment to meet the

loads is then determined by minimizing this

function with respect to D, and D,. This

minimum occurs when:

(7)

The optimum size of the plants is then

given by:

(capacity of baseload plants) = D1

(capacity of intermediate plants) = D2 – D1

(capacity of peaking plants) = P–D2

The approximate cost of generation for

the year is then given by using these quantities in equation [1 ).

Provision for Reserve Margin

Two major approximations have been

made in obtaining costs in this way: (1) no

provision is made for maintenance cycles,

the need to maintain reserve capacity for

unanticipated failures, and the need to

maintain some capacity as spinning reserve,

and (2) no provision is made for the costs

associated with starting or shutting off a

plant and the inefficiencies of running at

partial loads.

The first difficulty is handled by simply increasing the assumed capacity of each type

of plant by 20 percent. If the analysis shows

that an optimum size for baseload plants is

D 1

, it will be assumed that the utility actually installs baseload capacity equal t o

(1.2)D 1

. In actual utilities, these reserve

margins are computed by carefully analyzing the reliability and maintenance scheduIes of each plant in the system,

The second problem can only be eliminated with a detailed examination of the actual sequence with which plants are turned

on and off. However, this is beyond the

scope of this study. Choosing appropriate

average values for operating costs and efficiencies should produce results which are

sufficiently close to those of a detailed

model, and serve the purpose of looking for

major impacts of different load patterns.

Transmission and Distribution Costs

In addition to generating costs, the utility

will have expenses associated with transmission and distribution. These wilI vary greatly, since they are a function of the spacing

of the utility’s generating facilities and the

location of its customers. In this simple

model, it is assumed that the transmission

and distribution costs are in direct proportion to the utility’s peak generating capacity. While generating plants represent approximately 44 percent of the total value of

electric utility plants and equipment, approximately 60 percent of the new capital

invested by the electric utilities in recent

years has been invested in generating equipment and this trend is expected to continue

(see table V-2 in the main text). ’ 2 It is therefore assumed that for each dollar invested in

generating capacity the utility invests $0.67

in transmission, distribution, and other

equipment.

I n addition, the cost of maintaining transmission and distribution facilities is assumed to be proportional to the total investment

in such facilities. Maintenance of transmission and distribution equipment in 1974 cost

privately owned electric utilities in the

United States approximately 3.3 percent for

every dollar invested in such equipment.3 It

‘Statistics of Private/y Owned E/ectrlc Utllltles In the

United States, 1974, Federal Power Commlsslon, p xx I

226th Annual E Iectrlcal Industry Forecast, E/ectr/ca/

World, September 15, 1975, p 49

‘Statistics of Pr/vate/ y Owned Electrlc Ut///tles In the

United States, 1974, Federal Power Commission, pp

xxx VI, xxx vii, arrd xx I

2 fi-H 42 ( ) - 12
170 . So/ar Technology to Today’s Energy Needs

is therefore assumed that the annual transmission and distribution operating expenses

are 0.033 x (the investment in transmission

and distribution equipment) = 0.022 x investment in generating equipment).

The costs of generating facilities fuel

costs and operating costs actualIy used in

the analysis are summarized in table V-A-4.

Some of the characteristics of the solar energy equipment examined are summarized in

table V-A-5.

Table V-A-4.—Characteristics of Equipment Used in the Utility Model

1. Generation costs

Capital costs*

$/kW

Albuquerque

Nuclear . . . . . . . . . . . . . 796

Coal . . . . . . . . . . . . . . . . 691

Combined cycle . . . . . . 292

Boston

Nuclear . . . . . . . . . . . . . 845

Coal . . . . . . . . . . . . . . . . 713

Combined cycle . . . . . . 292

Fort Worth

Nuclear . . . . . . . . . . . . . 748

Coal . . . . . . . . . . . . . . . . 725

Combined cycle . . . . . . 292

Omaha

Nuclear . . . . . . . . . . . . . 769

Coal . . . . . . . . . . . . . . . . 668

Combined Cycle . . . . . . 292

Cycle Levelized fuel Variable

efficiency cost ($/kWh) O&M ($/kWh)

0.328 0.0056 0.00072

0.338 0.00682 0.00147

0.42 0.020 0.0012

0.328 0.0056 0.00072

0.347 0.00760 0.00189

0.42 0.020 0.0012

0.328 0.0056 0.00072

0.327 0.00456 0.00214

0.42 0.020 0.0012

0.328 0.0056 0.00072

0.338 0.00626 0.00148

0.42 0.020 0.012

Il. Transmission and distribution costs

O&M—O.022 of investment in generating capacity

Capital charges— 0.67 of generating capacity costs

Efficiency of T&D—O.91

Ill. Other costs

Cost of capital —O.15

Overhead–0.021 $/kWhr

20% excess generating capacity installed

“Capital costs include an allowance for “fixed operating costs” computed by dividing the fixed operating costs per

year by the Ievelized fixed charge rate.

SOURCE: Technical Assessment Guide, EPRI, August 1977. Statistics ot Private/y Owned E/ectric Uti/ities, 1974,

Federal Power Commission.

Table V-A-5.—Assumptions About the Nonconventional Systems Used in the Utility Impact Analysis

1. Albuquerque

Single family house

–SF-2

Flat-plate collector—30m2

Thermal output

Low-temperature storage—200 kWh

–SF-2

East-west axis tracking collector—92m2

Photovoltaic and thermal output

Low-temperature storage—200 kWh

Battery storage—23 kWh

—IF-2

Flat-plate collector—59m2

Photovoltaic output

Battery storage—20 kWh

–SF-3

Flat-plate collector—30m2

Thermal output

Low-temperature storage—200 kWh
Table V-A-5.—Continued

–SF-3

Off peak purchase of electricity y

Flat-plate CoIlector—30m2

Thermal output

Low-temperature storage—232 kWh

High rise apartment buildings

—HR-2

East-west axis tracking CoIlector—

4,263m2

Photovoltaic and thermal output

Low-temperature storage— 17,000 kWh

Battery storage– 170 kWh

Il. Boston

Single family houses

—SF-2

Flat-plate collector—45m2

Thermal output

Low-temperature storage—200 kWh

–SF-2

East-west axis tracking collector—92rn2

Photovoltaic and thermal output

Low-temperature storage—200 kWh

Battery storage— 12 kWh

—IF-2

Flat-plate Collector—59m2

Photovoltaic output

Battery storage—20 kWh

High rise apartment buildings

—HR-2

East-west axis tracking collector—

4,263m2

Photovoltaic and thermal output

Low-temperature storage— 17,000 kWh

Battery storage— 170 kWh

Ill. Fort Worth

Single family houses

—SF-2

Flat-plate collector —40m2

Thermal output

Low-temperature storage—200 kWh

—SF-2

East-west axis tracking collector—92m2

Photovoltaic and thermal output

Low-temperature storage—200 kWh

Battery storage— 12 kWh

–IF-2

Flat-plate collector—59m2

Photovoltaic output

Battery storage—20 kWh

Iv.

Appendix V-A ● 1 7 1

High rise apartment buildings

–HR-2

East-west axis tracking collector—

4,263m2

Photovoltaic and thermal output

Low-temperature storage— 1,700 kWh

Battery storage— 170 kWh

Omaha

Single family houses

–SF-2

Flat-plate collector—40m2

Thermal output

Low-temperature storage—200 kWh

–SF-2

East-west axis tracking collector—92m2

Photovoltaic and thermal output

Low-temperature storage– 12 kWh

–IF-2

Flat-Plate collector—59m2

Thermal Output

Low-temperature storage—200 kWh

–SF-3

Off peak purchase of electricity y

Low-temperature storage—31 3 kWh

–SF-3

Off peak purchase of electricity

Flat-plate collector—40m2

Low-temperature storage—293 kWh

High rise apartment buildings

—HR-2

East-west axis tracking collector—

4,263m2

Photovoltaic and thermal output

Low-temperature storage— 1,700 kWh

Batteries— 170 kWh

—HR-2

(seasonal storage)

Flat-plate collector—4,100m2

Thermal output

Low-temperature storage—

1,200,000 kWh

NOTE: SF-2 single family house with heat pump and

electric hot water.

IF-2 well-insulated single family house with

heat pump and electric hot water.

HR-2 high rise apartment buildings with central

electric chiller, for coil resistance heating,

central electric hot water.

SF-3 single fmaily houses with window alrconditioners, baseboard resistance heating,

and electric hot water.

SF-3 off peak heating and hot water (with or

without solar), window alr-condit ioners,

electric resistance furnace, and electric hot

water.

SF-3 off peak heating, coollng, and hot water

(with or without solar), central electric

chiller, electric resistance furnace, and

electric hot water.
Chapter VI

LEGAL AND REGULATORY ASPECTS

OF ONSITE SOLAR FACILITIES
Chapter Vl.– LEGAL AND REGULATORY ASPECTS

OF ONSITE SOLAR FACILITIES

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

Solar Rights: Protecting Access

to Sunlight . . . . . . . . . . . . . . . . . . . . . . . . . .176

Introduction. . . . . . . . . . . . . . . . . . . . . , .. ...176

Existing Laws: Adequate Sunright

Protection?. . . . . .................,.176

NewDevelopment. . ..................176

Zoning . . . . . . . . . . ..................176

RestrictiveCovenants. , .............176

Express Easements. . ...............177

Land-UsePlanning . ................177

TransferableDevelopment Rights. ... ...178

Existing Developments. . ..............178

Should the Federal Government Enact

National SolarAccessLaws?. . .......178

Status of State Legislation . ..............179

Building Codes and SolarSystems . .........180

Introduction. . . . .......................180

Do the Model Building Codes

CoverSolarSystems?. . .............181

What Solar System Standards

Are Needed? . .....................182

Page

What Position Have Building Officials

Taken on Solar Facilities? . ..........182

State Standards. . ....................183

State Certification. . ..................183

OnsiteSolarFacilities and Public Utilities. ...184

Introduction. . . . .......................184

Utilities: DoRates or Service

Practices DiscriminateAgainst

OnsiteSolarUsers?. . ...............184

Conventional RateStructure . ..........184

Selling Energy to a Utility. . ............186

RegulationsCovering Discrimination ....187

AreOnsiteSolarSystemsSubject to Regulation as PubiicUtilities? . ...........190

Ownership . .........................191

Electricity, Steam, or Heat? . ...........192

Can a UtilityOwnanOnsite Solar Facility? .192

Municipal Utilities. . ..................194

Cost-Sharing Issues . .................194

What RightsWill Utilities Have to

Aquifers and OtherGeological Formations Used for Thermal Storage? .. ....195
Chapter VI

Legal and Regulatory Aspects

of Onsite Solar Facilities

INTRODUCTION

Onsite solar facilities are controlled by laws and regulations often written

with entirely different energy systems in mind. That being the case, this study

finds surprisingly few barriers to large-scale installation and operation of onsite solar facilities. Existing legal barriers are almost entirely inadvertent.

These barriers can delay the introduction of solar equipment, but in most

cases they can probably be removed with routine regulatory action.

Resistance to changes in zoning or building codes, for example, generally

arises when an interested party will be adversely affected. It is not likely that

builders, owners, labor unions, or public officials will perceive onsite solar

generation as a threat.

The exceptions to this generally optimistic conclusion are the laws and

regulations governing public utilities. Most statutes and regulations governing energy generating equipment assume that energy would be supplied

primarily by large regulated utility companies which would enjoy a “natural

monopoly” in a given region. If small facilities become economically competitive, however, the only natural monopoly may be systems for transmitting

and distributing energy. It is important to notice that most of the regulatory

issues raised in connection with small solar energy devices also apply to conventionalIy powered on site cogenerating equipment.

Application of existing utility regulations to onsite energy systems is frequently ambiguous, sometimes contradictory, and occasionally inadvertently

discriminatory. Problems can arise if utilities attempt to own and operate onsite equipment, and if organizations other than utilities attempt to generate

solar energy for sale. Regulations governing the rates charged by utiIities for

backup power and the price at which they will be willing to purchase onsite

power generated in excess of onsite needs can have an enormous effect on

the cost of solar energy computed by nonutility owners of solar equipment.

Existing rate structures, however, have been designed without attention to

the problems of solar equipment and the analytical basis for determining

equitable rates is only beginning to be established. Although regulated

natural gas prices were designed to benefit gas consumers, the policy tends

to reduce the attractiveness of solar energy devices.

How these ambiguities are resolved can have profound effect on the future

of the solar energy industry. Regulations can affect the designs chosen and

patterns of ownership, and they can serve to retard, stifle, or stimulate the

development of the industry. It is clearly an area where doing nothing could

translate into a policy of restraining the growth of the solar industry.
176 Ž So/ar Technology to Today’s Energy Needs

SOLAR RIGHTS: PROTECTING ACCESS TO SUNLIGHT

INTRODUCTION

An investment in a solar installation must

be considered insecure unless the owner can

be assured that the collectors will not be

shadowed by new construction or vegetation during the useful life of the equipment.

Protecting this access to sunlight can be difficult, since no property owner in the United

States has an absolute legal right to sunshine.

1 If procedures to ensure some such

protection cannot be developed, concern

about “sun rights” could present a major

barrier to the use of solar energy, It may not

be easy to provide such protection in densely populated areas or in areas graced with

large trees, In some cases–particularly older residential neighborhoods — it may be impossible to ensure access to sunlight for all

buildings. A considerable amount of protection can be provided, however, with imaginative use of existing laws, zoning ordinances, and covenants; it seems unlikely

that additional Federal legislation would be

able to contribute usefully to the resolution

of these problems.

EXISTING LAWS: ADEQUATE

SUN RIGHT PROTECTION?

New Development

Imaginative work is needed to determine

how best to use existing laws. Although local

governments are able to help protect sunrights, under existing statutes this power

usually is not used to help solar equipment

owners.

ZONING

The power to zone can literally shape a

community from broad outline to minute

detail, The zoning authority power is broad

enough to enable States and municipalities

to assure solar access in new subdivisions,

shopping malls, industrial parks, and small

community developments, Existing zoning

reguIations may direct the purpose for

‘ Fountainb/eau Hotel Corp. v Forty-five Twentyflve, /nc,, 114 So. 2d 357,181 Fla Supp 74 (1959)

which land may be used, control building

heights and orientation, and govern lot

sizes, yard requirements, the appearance of

buildings, property, and secondary structures.

If maximum use of solar collectors is

desirable, it may prove useful to adopt mandatory minimum or uniform height regulations similar to rules that now limit building

heights. ’ Since zoning laws generally allow

underdevelopment, problems are foreseeable. For example, if a property owner in an

area zoned for 16-story development builds

only a 4-story building, shading problems

could ensue. Perhaps economic incentives

wiII make such cases rare.

RESTRICTIVE COVENANTS

The numerous local building covenants

and architectural review boards provide

another opportunity for protecting sun rights

in a community but may also present problems for solar equipment. These covenants

are private legal devices which are typically

in the form of reciprocal promises in each

deed of a subdivided tract. They can be

used to provide detailed guidance about the

kinds of architecture and the building

materials which will be permitted in the

region covered. Since many early solar collectors are likely to be ungainly (if not

outright ugly), it is possible that the use of

solar devices will receive unfavorable treatment by local organizations reviewing compliance with the building covenants. The

problem is Iikely to become much more difficult if tracking collectors begin to enter

the market in significant numbers. The unattractive appearance of the inexpensive solar

water heaters in Israel has apparently

presented a major problem for manufacturers in that country, and there are isolated

* Such a law may guarantee each structure

enough sunlight for a hot water heater or other roof

collectors, but would obviously not meet the needs of

vertical solar collectors (includlng windows) that are

part of a structure’s wal Is
Ch. VI legal Aspects of Onsite Solar Facilities ● 1 7 7

instances of local opposition to rooftop

solar systems in the United States. It r-nay be

useful to anticipate the problem and

develop regulations which would permit

solar facilities in which some care has been

taken to minimize pipe-farms on rooftops

while permitting enough flexibility in design

to ensure efficient performance of the

equipment. Clearly, there will have to be

some compromise between performance

and aesthetics.

The advantages of using restrictive covenants as a means of protecting sunrights

are threefold: (1) covenants can be used to

thwart impending interference of solar access (usualIy by injunction) before construction begins, thus assuring a continuous supply of sunlight; (2) they cost the Government

nothing; and (3) State or local governments

could encourage or require their use in new

developments.

EXPRESS EASEMENTS

Express easements provide another private legal device to protect access to sunlight in both new and existing developments.

An easement confers the right to use (not

possess) specified parts of another’s property for a special purpose. A property owner,

concerned about shading, could bargain

with a neighbor for an unimpeded path of

sunlight over the neighbor’s land. Easements, which may also be leased, are binding on subsequent owners of both parcels i n

many States, but in others new legislation

may be necessary to assure continuity of access to sunlight. Something of value is traditionally given in exchange for land (although

some courts don’t require it), and the agreement must be in writing to be enforceable.

if a State views easements for light and air

as benefiting a person (i. e., “in gross”) rather

than a parcel of land, the State may not enforce the agreements against subsequent

owners, although a subsequent owner probably could, To attain enforcement, a State

can enact a short, simple statute stating that

such easements must include the vertical

and horizontal angles over adjoining property; terms and conditions of the grant; and

any compensation to be paid to any party involved. The legislation should also assure

the recording of express solar easements

along with other land records.

Colorado has already enacted such legislation, and Florida, Maryland, and Arizona

are considering nearly identical bills.

The advantages of express easements are:

they cost governments almost nothing; they

allow highly motivated individuals to act on

their own; they may offer more protection

than zoning laws, which can be changed;

and they are adaptable to specific needs of

different property owners.

Disadvantages are their transfer with the

sale of land cannot be forced, their cost is

uncertain, enforcement through the courts

could be costly, and the would-be owner of

a solar structure must bear the entire cost of

an easement.

LAND-USE PLANNING

Commonly used techniques that could

promote solar utilization in new developments include comprehensive city or county

plans, energy impact statements, and flexible zoning techniques.

Many States use comprehensive plans to

guide long-range policy in local zoning.

Some State courts require that local zoning

agree with a comprehensive plan. At least

two States have considered including solar

energy elements in their comprehensive

plans.

Nine States require that environmental

impact statements discuss the effects of

projects on energy consumption — two require analysis of measures to conserve energy resources,2 The developers of large tracts

of land must usually file impact statements

under State laws, and this procedure might

be used to assure consideration of solar

energy utilization. Colorado has considered

‘ Corbln Crews Harwood, Us/rig Land to Sa\e Energy (Carnbrldge, Mass Balllnger Publlshlng Co , forthcoming)
178 ● Solar Technology to Today’s Energy Needs

such a bill.3 The same Colorado bill would

require that subdivision regulations include

standards and technical procedures for solar

use.

Flexible zoning techniques include

planned unit developments (PUDs) and

bonus or incentive zoning. Only a few States

specifically authorize PUDs, but some communities use this technique without State

authorization. This concept relaxes zoning

requirements and allows builders to offer

layout, building design, and uses as a single

package.

To obtain approval of their plans, developers could be required to indicate where

shadows would exist and to justify designs

that would create shadows. Bonus or incentive zoning offers governmental rewards in

exchange for a developer’s inclusion of

design elements otherwise not directly required by zoning.

Transferable Development Rights

A much-discussed but little-used approach to land-use planning called transferable development rights (TDR) is uniquely suited to protecting solar access.

Under the TDR concept, rights for development conferred on lots by zoning codes

are transferable and can be sold independently of the land. Property owners could sell

development rights that they could not exercise because of solar restrictions. For example, the owner of a commercial property

that adjoins a neighborhood of single family

homes might sell the right to build a tall

building to the owner of a lot where a tall

building would not cast shadows on solar

equipment. Under this concept, a municipality can be a buyer-of-last-resort for development rights in cases where it is necessary to

protect access to sunlight for solar collectors The main advantage of the TDR concept is that it permits a municipaIity to

police solar access rights and avoid unconstitutional taking of property without compen sat ion.

‘ (010 H B 1166(197’6)

The Los Angeles Department of City Planning concludes that its code may be adequate to protect solar access in developed

as welI as new neigborhoods, 4 Transition

neighborhoods, where new commercial development is allowed alongside older residential sections, will be one of the most

difficult areas in which to protect solar access. If a newly zoned commercial area is

south of an older residential neighborhood,

the taller buildings may cause shading problems. Los Angeles zoning regulations deal

with this by Iimiting new structures in such

areas to six and three stories, “stepping

down” heights gradually to avoid sharp contrasts between old and new development. 5

Existing Developments

Assuring the protection of sunrights in

neighborhoods can be a difficult problem.

Many existing buildings in older commercial

areas probably could not be adapted to use

solar energy unless basically rebuilt, which

means the demand for solar access in these

areas may be small. Clearly, it would be

desirable to consider solar access when an

entire area is to be redeveloped, or even

when individual permits for remodeling are

issued,

Probably the strongest available technique for protecting sunrights in existing

developments is the purchase of solar easements. It may be possible (for a price) for a

prospective solar owner to purchase an

easement that will require his southern

neighbor to cut trees to provide access to

sunlight.

SHOULD THE FEDERAL GOVERNMENT

ENACT NATIONAL SOLAR ACCESS LAWS?

The Federal power to regulate commerce

and provide for “the common defense” is

4 Charles S Rozzellee, Property Owners’ R/ghts to

SurJ//ght, Los Angeles Department of City Planning,

City Pldn Case No .26110 (1976), see p 14

5 I bid , p 12 An admlnlstratlve problem could

arise If the city were flooded with applications for

these special zones
Ch, V/ Legal Aspects of Onsite Solar Faci/ities ● 179

apparently broad enough to allow Congress

to adopt policies protecting the use of solar

energy if it so desired. b It is probably not

necessary (and may even be unwise), however, for the Federal Government to intervene in protection of individual access to

solar energy

Solar rights laws will have to be adapted

to local conditions, no matter wher e

drafted The variables that must be considered in access laws include topography,

latitude, availability of alternative energy

sources, long-term regional growth plans,

impacts of past and present zoning laws,

and even the relationship of streets to

sunlight patterns.

It is possible, however, that State or

Federal encouragement will be needed to

motivate local governments to incorporate

solar access into their statutes. One expert

estimated that only 5,000 of 60,000 jurisdictions with power over land use exercised

zoning powers in 1974 7

While preemption seems unnecessary, an

appropriate Federal role might be a national

policy set by Congress. For example, the existence of solar access laws could be a factor in choosin g locations for federally

owned, funded, or operated structures.

‘ \t Ickard \ I l/burn, )1 7 U S 111 (1 942), a person

grow I ng wheat on hl~ own land tor home use — a noncom m erc I d I dct I v I t} — w a $ tou nd to have enough ef -

tec t on Interstate commerce to come under the Congress’ power

7 Peter Welt, The Future oi the City N’ew Dlrcctjons (n Urban P/annln~ (New ‘r’ork Wa tson-Gupttl I

Public atlon~, Whitney Library ot Design, 1974), p 149

“ Crlterid \pPc I tIC J I Iy referring to solar ac( es<

cou Id be ~ dded to H U D’~ Se{ t Ion 701 Cornmunlty Devel opmen t prog rd m, w hlch provides financing for

land-u~e plannlng that meets certain ( rlteria Sect Ion

701(C) ot tire Flous[ng Act ot 1954 (ds dmended by the

tiouf~ng dnci Commurllty Development Act of 1974)

\ays that tu nd 5 w I I I on I y be ava I I a b I e t o ap p I I c d nt ~

w ho have on go I ng co m prehen $ Ive p I d n n i ng p roces~es

that Inc I ude both a housl ng element and a I and use

e I e me n t The o~era I I a I m of t h Is program I \ corn pat Ible with the encou rdgement of \ol ar-ac ce~~ pl ann I ng,

‘5 I n cc It hopes to en( ou rage ‘‘a more rat Iona I ut I I I zd -

t Ion ot land and other natural resources, and the bette r a r rd ngement of res I den t I d 1, com m e rc I a 1, I nd u jSolar access criteria could be added to the

Department of Housing and Urban Development’s (HUD) Section 701 Community Development program, which provides financing for land-use planning. 8 The overall aim

of this program is compatible with the encouragement of solar-access planning, since

it is designed to encourage “a more rational

utiIization of land and other natural resources and the better arrangement of residential, commercial, industrial, recreational, and other needed activity centers, ”

STATUS OF STATE LEGISLATION

A variety of legislation has been proposed

on the State level. A bill in Massachusetts

(Senate No. 269, 1977) uses the building permit system to protect sunrights. Under this

proposed law, those wishing to erect activeor passive-type solar energy units would

have to reasonably locate and angle their

equipment to minimize the possibility of

future interference with it, To get a building

permit, the equipment also would have to

be reasonably sized relative to the structure.

The remaining problem of vegetation in adjoining property would have to be solved by

express easement. In land zoned for developments for four stories, the municipal plantrla 1, recreat Iond 1, and other needed a( t I\ Ity center$ “

The regulations accompanying the 701 progralm (Title 24, part 600 — Comprehen~lve Plannlng As$lstance)

halve been dmended to emphd~l~e energy concern~

Se( tlon 60072 now state~ that In $ele( tlng prlorlttes,

edch reclplent shou Id con~ tder

(,2) Prolectlonsof land use needs and land resource

development Includlng energ} tac I I ltl~s sltl ng

needs

(7) The conservdtlon of energy through land use

~trdtegles des Igned to reduce energy consu mp

tion and the development of pol I{ IPS designed to

tac I ! Itate the re{ oier~ ot energy re$ourc e$ I n d

manner ( ompdt Ible with environmental I protec

t [on

“ Energy tacll Itle> sltlng needs” could be Interpreted

to lncl ucle “talc I I ltle~” a~ ~ma I I as an drrdy ot ~old r c olIectors on the roof of a ~lngle it ructure, but a more expl I c It ~tatutory conslderdt Ion of Jol a r energy needj I \

rea I Iy needed

42 u s c 5301 (c) (5)
180 . Solar Technology to Today’s Energy Needs

ning agency and the municipal governing

body would have to approve a proposed

solar structure. Before a nonsolar structure

could receive a building permit under this

legislation, the records would have to show

that there was no interference with an approved solar collector.

A Minnesota bill suggests a very different

legal approach (Minnesota H.R. 2064, 1976).

It would simply grant solar easements to any

collector owner. Anyone erecting an object

shading the system would have to pay the

solar homeowner three times the actual cost

of implementing an alternative energy

system. Although the penalty section is intriguing, this bill has many problems, including vagueness and unfairness based on

the first-come, first-served basis of the law.

Colorado legislation would forbid property owners from allowing their trees and

shrubs to grow enough to shade solar collectors between 9 a.m. and 3 p.m. ’ But it is an

attempt to deal with the serious problem of

vegetation, and the specific times listed i n

the legislation give property owners a clearer view of their rights than a vague protection of “sunlight necessary for the operation

of solar equipment. ”

The tiny town of Kiowa, Colo., has enacted a law declaring shadows on collectors

to be public nuisances. This nuisance approach could present several kinds of problems: no certainty of protection would exist

before a collector was installed, tangled

complexity of the nuisance law, and costly

Iawsuits

putes.

Law

., -.&- -

propr

rev iv i

lights

either

would be required to settle disjournal articles suggest applying

laws used in the West — the prior apiation doctrine — to solar access, and

ng the old English doctrine of ancient

10 11 No State has, to date, followed

of these suggestions, both of which

would require extensive litigation, provide

no compensation to the injured solar users,

and were not drafted specifically for solar

applications.

BUILDING CODES AND SOLAR SYSTEMS

INTRODUCTION

Building codes, specifically applicable to

hot water and space heating, air-conditioning, and electrical equipment, seldom

contain provisions covering onsite solar

systems. Code problems do not appear to

have been a major barrier thus far, but it is

clearly possible that uncertainty on the part

of code officials resulting from a lack of information about solar devices and a shortage of standards and certification procedures for solar systems could result in

‘ Colorado S B 38 (1976)

‘0 Mary D White, “The Allocation of Sunllght Solar Rights and the Prior Appropriation Doctrine, ”

University of Colorado Law Review 47 (1976) See t h e

extensive review In the E nvlronmental Law Institute’s

(E Ll) Legal Barriers to Us/rig Solar Energy for Hearing

and Cooling f?ui/dings, which was contracted for by

fragmentation of the solar market, delays,

additional expenses, and uncertainty to the

builder or owner in the permit application

and process. There are, as a result, compelIing reasons for enacting mechanisms for

inspecting solar equipment similar to those

in effect for other heating, cooling, and

generating equipment installed in residences or commercial buildings.

The Federal Government, in a HUD demonstration program, developed standards

the Energy Research and Development Admin[stratlon, and IS an early effort In this direction It is

available from E L I (1 346 Connecticut Ave , N W ,

Suite 620, Washington, D C 20036) for $750

1‘ Lawrence Kressel, “Harrsorr v Sa/is/ran Properrles,

/rrc,, Preservation of View– Limltatlons as to Height

of Improvements and Architectural Control In Uniform Long Term Lease, ’’fnv. Law5(1974) 183
Ch. VI Legal Aspects of Onsite Solar Facilities ● 181

that could be used as models for incorporation in building codes. Certification that

solar systems meet those standards could be

delegated to approved testing agencies,

thereby expediting the building permit process for solar users.

DO THE MODEL BUILDING CODES

COVER SOLAR SYSTEMS?

The three most widely used model building codes are:

●

●

●

The Basic Building Code of the Building

officials and Code Administrators

(BOCA), found mostly in the East and

Midwest;

The Uniform Building Code of the International Conference of Building Officials (ICBO), found mostly in the

West; and

The Standard Building Code of the

Southern Building Codes Conference

(SBCC), found mostly in the South.

According to a 1970 survey of local

building departments, 63 percent of the 919

cities that had building codes of any kind

used one of these three model codes. 1

2

The most widely used standards for electrical wiring and equipment are those of the

National Electrical Code of the National

Fire Protection Association. Although no

exact figures are available, it appears that

these electrical equipment standards are

even more widely used than any of the three

major model building codes. The electrical

standards are adopted by reference in the

BOCA code (Section 1500.3), but not by the

other two model codes.

Building codes define terms, set standards

for materials and equipment, describe how

materials and equipment may and may not

be put together, and provide for enforcement through permits and inspections.

Standards generally are either specification

‘‘ Charles G Field and Steven R Rlvkln, The

EluI/ding Code Burden, Lexington, Mass D C Heath

and Co , Lexington Books, 1975, p 43

standards, which identify materials and

equipment that may be used in construction, or performance standards, which set

standards that materials must meet. Specification standards are easier to administer,

but are inflexible. Performance standards

are more flexible, but require more trained

personnel, time, and money to administer.

Building codes regulate nearly everything

that is constructed or built on land, with few

exceptions. Before granting permits for construction, remodeling, or repairs, buiIding

officials decide whether plans conform to

code requirements. If a plan proposes use of

materials and methods that are specifically

covered by a building code, approval is routine. If a plan calls for innovative materials

or techniques, however, a building official

has the discretion to require testing of materials and submission of evidence that the

resulting structure will not be inferior to a

traditionalIy built structure.

Most building officials display wide

latitude in approving or rejecting materials,

equipment, and methods not specifically

provided for in the codes. If alternativ e

materials or techniques are to be used,

building officials must be satisfied that the

resulting structure will be at least equal in

strength, fire resistance, safety, quality, and

effectiveness to structures assembled with

materials and techniques specified in the

code. I n such case-by-case showings, applicants may be required to pay for testing

at facilities chosen by the building officials,

using methods approved under the codes or

chosen by them.

For most kinds of construction materials

and equipment, nationalIy recognized

standards, test methods, and testing agencies are specified in the codes. Two examples are the Underwriters Laboratories,

Inc., for electrical equipment, and the American Gas Association, for gas equipment, For

solar energy systems such nationalIy recognized standards, test methods, and listing

agencies do not exist.

Under al I three model codes, heating, ventilating, and cooling appliances must be ap-
182 ● Solar Technology to Today’s Energy Needs

proved by building officials or carry the

label of an approved testing agency or laboratory. A “heating appliance” is presently

defined in all codes as a device that generates heat from sol id, Iiquid, or gaseous

fuels, or with electricity, Solar sources are

not mentioned, nor are they included in the

definitions of ventilating or cooling appliances. In addition, there is no agency to

certify compliance and attach labels to

solar equipment, nor is there a nationally

recognized set of standards on which to

base compliance. Solar heating systems are

therefore at a potential disadvantage as

compared to conventional systems, which

can be approved for instalIation with a simple showing of a label.

Other possible impediments to the use of

solar facilities include code requirements

for maintaining rather high minimum building temperatures in cold weather, and formulas for determining window sizes. Limitations on awning and roof overhangs may interfere with some passive solar designs.

Standards for prefabricated assemblies may

result in costly tests to demonstrate weather

resistance.

More potential problems include limitations on residential building heights that

may preclude roof collectors, chimney and

plumbing clearances, application of new

standards to remodeling of old buildings,

and implied prohibitions against using solar

colIectors as integral parts of a structure’s

roof or walIs,

WHAT SOLAR SYSTEM STANDARDS

ARE NEEDED?

The only unique component of solar

heating, cooling, and generating systems is

the collector. Once heat is collected, or

electricity is generated, it is transported,

stored, and utilized by the same type of

equipment used in conventional systems.

Standards for pipes, ducts, valves, storage

tanks, controls, wiring, storage batteries,

and other components already exist, even

though their use in a solar energy system

was probably not contemplated when the

standards were written. The primary requirement for new standards is for solar collectors, including photovoltaic and focusing

devices.

Problems could result from novel usage

of equipment and materials presently covered in the codes, involving risks of leakage

or explosion from excessive temperatures,

high pressures, corrosion, and other component failures. Standards should address

these and other risks, including human contact with hot surfaces or broken glass, contamination of drinking water with toxic

coolants if plumbing is not properly installed, and damage to collectors from high

wind or heavy snowfalIs,

These risks would be relatively low in systems designed for low-temperature uses,

such as heating buiIdings or drying grain,

but could be higher in some proposed solar

electric systems. Building codes must be

amended in ways that apply different standards for material and equipment according

to the use of the solar energy facility.

WHAT POSITION HAVE BUILDING

OFFICIALS TAKEN ON

SOLAR FACILITIES?

Few builders have reported difficulties in

obtaining building permits to construct solar

facilities. The major problem with codes

may prove to be an overly lax inspection

resulting from untrained inspectors rather

than codes so strictly written that they interfere with sound solar engineering. Building codes expert Steven Rivkin has said that,

“Rather than serving as a retardant, existing

building codes have no bearing at all on the

development of solar systems.’’13It is possible that building officials will continue to

look with favor on solar energy systems, and

not rigidly enforce codes.

As solar energy systems gain in popularity, some kind of additional code require-

‘ ‘ AlA Research Corporation, Early Use of Solar

lnergy In Buildings, 2 Vols , Washington, D C , August

1976, 211-32
Ch. VI Legal Aspects of Onsite So/ar Facilities ● 183

ments will need to be developed. Without

specific coverage in model building codes,

however, local interpretations of plans or requirements for costly testing could fragment

a potential market, result in higher costs of

solar devices built to meet the strictest

standards found anywhere, and delay building and construction of solar systems.

All appliances face this problem at some

time, and the solution has been nationally

recognized standards and testing procedures for the various models of equipment

and materials Applying the same procedure

to solar equipment would put solar energy

systems on the same footing as other heating and electric systems

Most building codes are enforced at the

local level, often with guidance from State

laws but seldom with intervention at the

Federal level. As has been noted, where

codes are in effect, the majority of communities adopt and adapt the model building codes. The first step toward assuring acceptance of onsite solar facilities as standard equipment is to draft a model set of

standards for inclusion in the major building

codes. The second is to designate a testing

agency to certify performance of solar energy systems.

The effort to develop national standards

couId be coordinated by the Federal Government There is precedent for this, including an ERDA contract with the National

Conference of States on Building Codes and

Standards to develop a model code for energy conservation in buildings.

The Federal Government has already developed standards for commercial and residential solar facilities as part of a solar heating and cooling demonstration program administered by HUD. These standards, or

some variation of them, are avaiIable for incorporation in building codes.

A final Federal role in amending the codes

would be to encourage State adoption of

standards for solar equipment Federal legislation mandating, encouraging, or providing

incentives for State regulations or standards

for solar equipment would function within

Congress’ power to regulate interstate commerce,

Certification is another matter. Federal efforts to certify solar appliances under its

HUD standards met with some criticism, and

the Federal Government has traditionall y

been reluctant to favor one commercial

product over another. However, because

some approved testing agency must be

designated as the solar industry grows, the

Federal Government might provide seed

money for expanding an existing testing

agency or creating a new one.

State Standards

States can write their own solar equipment standards, with variations based on

State and local conditions, provided that

they do not unreasonably burden interstate

commerce, One approach would be to

adopt standards similar to those already

drafted by the Federal Government under

the HUD program, on an interim basis, until

private-sector standards have been approved. A recently enacted Minnesota law

takes this approach, It requires a State agency to promulgate standards for solar heating

and cooling systems based on current interim Federal criteria. 14 The law also requires State administrative agencies to update State standards as new Federal standards are adopted or as new technology dictates.

State Certification

States will want to assess the suitability of

solar equipment as to safety, health, structural strength, and adaptability to State or

local building codes. The Florida Solar Energy Center in Cape Canaveral already is testi ng and certifying the thermal performance

of colIectors sold in that State As an interim

measure, State certification can provide

local building officials with guidelines until

a national testing and certification program

‘4 Mlnn Stat ~116 H 127 (1976)
184 . Solar Technology to Today’s Energy Needs

can be put in place. Some States may wish

to go beyond furnishing guidelines, and can

write laws that require local building officials to approve solar equipment that

meets State standards and is certified by

State agencies.

ONSITE SOLAR FACILITIES AND PUBLIC UTILITIES

INTRODUCTION

State laws and regulations governing the

relationships between public and private

utility companies and the owners of onsite

generating equipment are complex, and frequently ambiguous, largely because these

problems have seldom been addressed by

regulatory commissions. I n the small number of cases where utilities and industries exchange electrical power or process heat,

contracts have generally been written in

ways benefiting both parties so that no

lawsuits have been brought forcing the

courts to rule on ambiguities in the law.

The following discussion examines the

statutes and regulations that now govern

relationships between public utilities and

onsite generators of solar energy, and outlines areas where ambiguities exist. It is an

attempt to highlight areas where major regulatory problems may exist.

State regulation through State public utility commissions is the primary issue. Federal

power authority has been limited to regulation of wholesale rates of interstate sales of

electricity, and siting of hydroelectric facilities, and is of less concern in the following analysis. The onsite solar systems, by the

very definition of “onsite,” are seldom involved in interstate, wholesale sales,

although power sold to a utility grid may

reach interstate commerce.

UTILITIES: DO RATES OR

SERVICE PRACTICES DISCRIMINATE

AGAINST ONSITE SOLAR USERS?

Perhaps the most crucial question in utility regulation is whether utilities may adopt

rates or service policies that unfairly discriminate against solar customers requiring

utility power as backup.

The answer appears to be that current

laws will permit discriminatory rates for

solar customers if the utility can prove that

the cost of providing service to solar customers exceeds the cost of providing service

to other customers. Although it cannot arbitrarily set prices or refuse service in an

effort to eliminate competition from solar

devices, the burden of proving such discrimination may falI on the solar customer.

Difficulties are likely to occur only when

an electric utility is involved since gas utilities would, in general, not be adversely affected by a need to provide backup service

to onsite facilities. Calculating a rate for

both the purchase and sale of electric energy to a utility is an extremely complex problem. The technical and economic bases for

such rates are discussed in detail in chapter

V. The present chapter focuses exclusively

on the legal and regulatory mechanism for

setting rates.

Conventional Rate Structure

The price a consumer pays for electricity

seldom directly reflects the cost of producing it. I n the absence of widespread time-ofday metering, billings usually are based on

formulas that allocate peak costs of energy

and total monthly consumption according

to the historical demand patterns of different categories of customers.

The most common residential electric

rate is the “declining block rate, ” under

which customers are charged a fixed fee for

monthly service, with declining rates for

each incremental block of energy consumed
Ch. VI Legal Aspects of Onsite So/ar Facilities ● 185

beyond the amount covered by the fixed

fee. For example, the formula might call for

a charge of $3 for the first kilowatt hour

(kWh), $004 per kWh for the next 100 kWh,

and $0.03 per kWh for the next 200. (Examples of actual rate scheduIes in several

cities are Iisted in volume I I.) The declining

block rate was introduced when marginal

costs for electric utilities were declining and

utiIities were encouraging customers to use

more electricity. 15 Another frequent practice, designed to increase sales of electricity, is to reduce rates if a house or commercial buiIding is “al I electric. ”

Utilities justify using these rates in today’s

market by arguing that all-electric customers are more Iikely to use electricity during the night for heating and cooling than

are other types of residential customers,

who use electricity for Iighting and other

purposes during peak hours. ’6 The wisdom

of continuing a promotional rate schedule

in a period of declining energy reserves,

however, has been seriously questioned in

many quarters. President Carter’s proposed

National Energy Plan would have flatly prohibited declining block rates.

Declining block rates can discourage the

use of onsite solar power because a large

part of a customer’s utility bill is based on

the first few kwh delivered, power which

would probably not be replaced with solar

energy.

Larger utility customers are frequently

charged on the basis of their peak demand

during some specified period. Such rates are

designed to achieve a more direct relationship between consumption and the net generating capacity that must be installed to

meet the customer’s requirements, Techniques for determining peak demand vary

greatly. Some utilities charge according to

the peak demand during the previous 6 months, some take the lesser of monthly peak

demands, and some percentage of annual

demand, and others charge on the basis of

15 See Berl In, Cicchettl, and G Illen, Perspective on

Power, chapters 1-3

“ Letter Insert In monthly bill from Potomac Electrlc Power Company, January 1977

spot measurements of demand made without advance notice.

The impact of such demand rates on customers with onsite facilities can be very

great. In some cases, a demand charge

could be so high that a purchase of energy

at high rates, when onsite equipment failed

or when cloudy weather persisted, could

negate any savings attributable to the onsite

equipment for an entire year. The justice of

such charges is a difficult issue to resolve,

Providing power to backup random failures

of onsite equipment among a large number

of small customers can clearly be managed

without a large increase in a utility’s generating capacity. Relatively high backup

charges might be justified, however, if all of

these customers abruptly demanded backup

power during a prolonged stretch of adverse

weather.

Still another rate structure is designed to

provide standby service to customers who

do not use electricity under normal circumstances, although these rates would not

apply to solar customers under the current

definition of “standby power.’” 7 If the definition were changed to cover onsite facility

owners, however, the high minimum monthly charge associated with standby rates

would not be advantageous to customers

with onsite solar faciIities,

Some utilities have considered applying

demand charges to residential customers to

cover some of the market losses that would

be inevitable with widespread installation of

onsite solar generators. One such proposal

by the Public Service Co., a Colorado utility,

was fiercely opposed by solar customers, 18 19 who calculated that under such a

17 See, for example, Southern CalltornlaEdison’s

rate schedule #5 (standby rates)

18 Testimony of james H Ranntger, Manager of

Rates of Regu/atlon for the Publ IC Service Company of

Colorado Colorado Public Utllltles Commission lnvestlgatlon and Suspension Docket No 935, Sept

25-26, 1975

19 Testimony of Dr Ernst Ha bict, Jr , and Dr WilIlam Vlckery for the Environmental Defense Fund,

Colorado Public Utlllties Commission Investigation

(Op Clt )

2 d-H 42 { ) - 13
186 Ž Solar Technology to Today’s Energy Needs

rate structure a solar heating system that reduced energy requirements by 70 percent

would reduce electricity bilIs by only 35 percent. 20 The Colorado Utility Commission initially granted the utility’s request for the

rate change, but reversed the decision

following a rehearing and ruled that the

issue was sufficiently complex to be addressed in a generic rate hearing. ” 22

Lifeline rates have been adopted in a few

States. ” Under this system, the charge is low

for the first units of energy. The goal is to

ease the burden on low-income consumers. 24 This rate may incidentally benefit

solar users whose needs for supplemental

sources of energy are small enough to fall

within the “Iifeline” amount.

A final type of utility pricing is interruptible rates, This traditionally has been available only to industries willing to accept the

risk of service interruptions in return for

lower costs, Some studies have pointed out

that a solar user willing to accept the risk of

going without utility service on infrequent

occasions could save the utility substantial

amounts in capital requirements, justifying

a lower rate. I f the peak occurred onIy rarely, this alternative might be considerably

‘[) Gary MIIIs, “Demand for Electrlc Rates A New

Problem and Challenge for Solar Heating, ” ASH RAE

journal, january 1977, p 42

I’ In the matter of proposed Increased rates and

charges contained In tariff revlslons filed by Publlc

Service Company of Colorado, Declslon No 87460

(Colo. Pub Utll Comm’n , Oct 21, 1975)

“ Home Builders Ass ‘n of Metropolitan Denver v

Pub/Ic Serk Ice Co of Co/oracfo, Decision No 8957 3

(Colo Pub Utll Comm’n , Oct 26, 1976)

11 E g , Miller-Warren Energy Lifeline Act, 1975, Cal

Stats ch 1010 For other examples, see Energy Users

Report (f3NA), Dec 16, 1976, p A-25

‘4 See “Llfellne Rates – Are They Useful?”, Energy

Conservation Project Report, No 4 (January 1976), p

13 (ECP Report IS a publication of the Environmental

Law Institute, Washington, D C ) Some authorities

question whether the Ilfellne concept IS an effective

method to ald lower Income groups since these persons often consume relatively high amounts o f

energy

less expensive than additional units of storage or collector area. 25 The National Energy

PIan proposes that utility companies be “required” to offer interruptible rates to all

customers. 26

Selling Energy to a Utility

As of today, few utilities are willing to

purchase power from customers, although

special arrangements have been made with

several large industrial customers.27 I n some

cases, the price the utility pays for surplus

power reflects only the cost of the fuel the

utility would burn to generate an equivalent

amount of energy. I n other cases, the price

reflects both fuel costs and the cost of

equipment the utility would have to install

to generate the power. However, there are

so few arrangements for sale of surplus

power that clear patterns are difficult to

identify.

Southern California Edison Co., for example, recently proposed a rate schedule under

which it wouId buy energy from large industrial customers at “the lowest cost of

energy provided by any generating equipment in the BonnevilIe Power District.” 28

This is about 3 mills per kwh, a rate that

reflects a minimum energy displacement

fee. However, in the same proposal the utility offered to purchase energy from a Iimited

number of residential and smalI commercial

facilities at a rate that is essentially identical

to the rate the utility charges residential

customers. 29

The Gemini Co., which sells devices to

connect onsite wind generators and other

equipment to utility distribution Iines, iden-

‘5 Feldman and Anderson, Uti/ity Pr/cing, p 120

“ National Energy Act, SectIon 513

“ Thermo E Iectron Corporation, A Study of /rip/ant

Power Generation in the Chernica/ Petroleum Refining

and Paper and Pulp Industries, june 1976, U S Dept of

Commerce, NTIS PB-255-659

“ Southern California Edison rate schedul e

changes proposed In a letter to the Cal Ifornla Publlc

Utilltles Commission, Feb 2, 1977

‘9 Southern California Edison, op cit., Experimental

Schedule DC and AC
Ch. VI Legal Aspects of Onsite So/ar Facilities ● 1 8 7

tifies widely varying patterns of proposed

surplus-power prices. Some New England

utiIities are wiIIing to buy electricity at their

own sales price because fuel represents a

large fraction of their overall costs. Utilities

with low baseload fuel costs have been

more reluctant to buy surplus power. 30

Regulations Covering Discrimination

The rates just described were, except for

Colorado, not designed to discriminate

against solar equipment, although their impact is not diminished by the lack of an intent to discriminate.

One of the major purposes for public regulation of electric utilities is the prevention

of unreasonable discrimination or undue

preferences. 31 Nearly every State has a

statute prohibiting conduct that favors one

class of customer while harming another.

Typical statutes proscribe policies that are

“unreasonable,” “unjust,” “undue,” or “unlawful.’’” Discrimination is a question of

fact to be determined on a case-by-case

basis by the State utility commission, and it

is very difficult to predict precisely how any

given discriminatory practice will be analyzed,

As the previous chapter showed, determining fair rates for electric utility power is

an extremely difficult process. Uneven solar

demands on the utility can result in relatively poor utilization of expensive generating

and transmission equipment, but it must be

recognized that demands imposed by many

nonsolar customers are also very irregular;

the only fair measure of the cost of pro1

’

] Ben W/o If, Gernl nl Corporation, private communlcat Ion, Apr 17, 1977

‘) To e[ onoml$ts, “price dlscrlmlnatlon” IS valu e

neutra I and In( Iudes any case where the same product IS sold ~t more than one price For purposes of this

dlscusslon, “dlscrlmlnatlon” is used [n its more genera I 5en$e to refer to any dlstlnctlon [n favor of or

against a person The economists’ deflnltlon pinpoints

the I~~ue nicely what 15 the relevant “product” or

servl( e? The way the product IS defined WI]] determine a talr price

‘2 Priest, Prlnclp/es of Public Uti/ity Regulation ,

1 2/36-88

viding backup power to an onsite solar facility is to accurately compute the marginal

utility costs incurred in providing such

backup.

The parallel question involving a determination of the rate which the utilities can

be expected to pay for excess onsite power

offered for sale is equally difficult; several

very sensitive issues must be resolved. For

example, how shouId the costs of transmission lines be allocated between the price of

utility sales and the price charged by onsite

generators? Should the utility be expected

to purchase energy at rates reflecting the

marginal cost of providing the same amount

of energy from new utility equipment or

simply for the average cost of utility power

generated. It will usually not be possible for

utilities to pay a rate high enough to meet

typical industrial revenue requirements on

capital invested in new energy projects. It is

possible, however, that special rates could

be established which would permit utility

purchases at required rates, and it also is

possible that, if a utility could sign a contract with a firm guaranteeing purchases

over 10 to 20 years, the firm could accept a

smaller rate of return on funds invested in

the generating equipment. A simple technique for determining the amount which an

electric utiIity can pay for energy purchased

was discussed in the previous chapter.

I n general, the cases and State utility decisions suggest that utilities have substantial

freedom to treat different classes of customers differently. 33 Two general principles

3‘ See, e g , Re Paclflc Cas & E Iec Co , 9 P U R 3d 97

(Cal publ Util Comm’n 1955), Re promotional Actlvltles by Gas and Electrlc Companies, 68 P U R 3d

163 (N Y Pub Serv Comm ‘n 1967), Re Promotional

Practices of E Iectrlc and Gas Utllltles, 65 P U R 3d 40s

(Corm Pub Utll Comm’n 1966), lle City Ice & Fuel

Co , 260 App DIV 537, 23 N Y S 2d 376 (1940) But

utll Ity comm Isslons have not been reluctant to strike

down promotional practices they found to be of little

value to the utll Ity or the bulk of Its customers Re

Southwest Gas Corp , 61 P U R 3d 467 (Cal Pub Utll

Comm’n 1965), Re Carollna Power & Light Co., 52

P U R 3d 469 (N C Utll Comm’n 1964); Re Portland

General Elec Co , 67 P U R 3d 417 (Ore Pub Util

Comm’n 1967)
188 ● Solar Technology to Today’s Energy Needs

emerge: (1) preferential treatment is more

acceptable if it produces indirect benefits to

all customers; and (2) utilities may treat customers differently if there is a reasonable

economic basis for doing so, that is, costs to

the utility are clearly different. For example, discrimination in favor of solar users

that would reduce rates for all customers by

reducing the utility’s costs would be acceptable.

It seems clear that public utilities may

discriminate either against or in favor of onsite solar users if the discrimination either

benefits all customers or is based upon a

reasonable economic basis. Discrimination

could be either as service practices (e. g.,

specific times at which backup power could

be used) or as rate practices (e.g., higher

rates for less energy use).

A public utility is subject to State regulation in addition to antidiscrimination laws,

by virtue of being a public utility. Fun -

damental to the concept of a public utility is

its dedication of property to serve the public

without discrimination. AImost every State

has a statutory provision requiring utilities

to “furnish adequate and safe service,” 35

“provide such service, instrumentalities, and

facilities as shall be safe and adequate and

in all respects just and reasonable,” 36 o r

“furnish reasonably adequate service and

f abilities.”]’

A public utility “may not pick and

choose, serving only the portions of the territory covered by their franchises which it is

presently profitable for them to serve.” 38 A s

‘4 Priest, Principles of Public Utility Regulation,

128 8

‘5 Or Rev Stat $757020 (1974)

‘

b N Y Pub. Ser Law $65 (McKlnney)

‘7 WIS Stat Ann $196,03(1) (West) For a general

discussion of a utility’s duty to serve, see Note, “Utility’s Duty to Serve, ” Columbia Law Review 6 2

(1962) 312; and Donald P. Hodel and Ronald G.

Wendel, “The Duty and Responsiblllty of Oregon

Public Agencies to Provide Adequate and Sufficient

E Iectrical Utillty Service, ” Oregon Law Review 54

(1975). 539

with most issues in public utility regulation,

the duty-to-serve requirement is interpreted

on a case-by-case basis with “reasonableness” and the “public interest” as the

touchstones.

A public utility cannot refuse to provide

backup power to onsite facilities unless it

can demonstrate a compelling case that

backup service would cause substantial

harm to the utility’s existing customers.

Refusal to provide service would violate not

only Federal antitrust laws, but also the utility’s common law and statutory duty to provide utility service, Of course, the duty to

provide adequate service has some limits;

utilities may be excused from providing

service when prevented by acts of God,

labor disputes, and shortages of fuel supply. ” In some cases, utilities have been excused from providing service where to do so

would be unusually expensive, although

there is substantial precedent to the contrary."40

These laws would not, however, prevent

adoption of a policy which would discriminate against new utility customers who did

not use solar equipment. Existing statutes

appear to permit a regulation which would

prevent a utility from providing new service

to a customer not using solar energy equipment.

Some States have taken measures to restrict gas to certain customers or to eliminate its availability for some uses. For example, New York banned the use of gas in

swimming pools and in buildings without

adequate insulation. ” A few States have

banned its use in decorative lighting.

‘8 New York & Queens Gas Co. v McCall, 245 U S

345, 351 (191 8).

‘9 Priest, Principles of Public Utility Regulation,

a :237-238.

40 I bid., pp. 240-242.

4’ New York Pub. Serv. Comm’n, Case 26286 [Apr.

16, 1974]; and National Swimming Pool Institute v

A/fred Kahn, 364 N.Y S 2d 747,9 P U.R 4th 237 (1974).

See also “Ban on Heated Pools Leaves Californians

Boil lng,” New York Times, Feb. 5,1975
Ch. VI Legal Aspects of Onsite Solar Facilities ● 1 8 9

The legal principles involved in rate

regulation are similar to those discussed for

service discrimination. The same prohibitions on discriminating among customer

categories apply, as do the ambiguities as to

what constitutes “disc rumination.” 42

A rate structure that adversely affects

solar energy users, however, may be difficult

to challenge under current case law. Several

cases have upheld the legality of rate structures that subsidize a particular class of

customers (al l-electric customers) despite

antidiscrimination laws. I n 1965, a court interpreted an antidiscrimination statute as

barring only “unjust” discriminations, and

concluded that only arbitrary d incriminations are unjust:

If the difference in rates is based upon a

reasonable and fair difference in conditions

which equitably and logicalIy justify a different rate, It IS not an unjust discrimination 4 3

Part of the difficulty results from the fact

that the utility can argue that its cost structure justifies a discriminatory rate and the

chalIenger is hard-pressed to rebut the extensive analysis which can be conducted by

the utility about its unique cost structure,

although in cases requiring a calculation of

a fair backup charge for solar energy (and a

fair price to pay for excess onsite energy)

utilities can be as confused as the interveners.

41 Colorado Pub Utll Comm’n Declslon No 87640

(Oct 21, 1975), Leroy Fantasies, /rrc. v Swindler, 4 4

APP DIV 2d 266, 354 N Y 5 2d 182, 4 P U R 4th 334

(1974), appeal cfenfed, 34 N Y 2d 519, 316 N E 2d 884

(1974)

43 88 N j Super 233, 236, 211 A 2d 806, 808, 60

P U R 3d 210, 212

44 From 1956 to 1970, the average cost of electricity

In the United Stdtes decllned from 261 cents per kWh

to 210 cents While average rates decllned, the costs

of supplylng electricity to certain types of loads and

to customers during peak hours Increased rapidly

Utilltles subsidize some customers by overchargin g

others Since 1970, costs have Increased steadily; the

average cost per kWh in 1975 was 3 21 cents, despite

an equally steady rise In consumption during th e

same period Samuelson, “Reform of Electrlc Utility

Rates, ” p 1475 See a/so Paul joskow, “lnflatlon and

Until the late 1960’s, cost per unit of electricity for at least some types of powerplants

declined steadily, Utilities could therefore

argue that promotional rate structures

would, over time, bring new businesses that

wouId justify additional powerplants. These

new plants would then lower the bills of all

customers of the utility. More recently, the

lack of new sites for low-cost hydroelectric

power, changes in regulatory practices, and

increased environmental costs have forced

the cost of new power to rise steadily.44

In these circumstances, promotional rates

lose much of their appeal. A New York court

recognized the common impact of rising

fuel prices in a recent decision overturning a

subsidy for all-electric homeowners. 45 The

subsidy, which was to run for a year, was intended to lessen the impact of higher electric rates on residential customers who had

previously been induced to buy all-electric

homes by favorable rates. The court held

that the subsidy “constituted undue preference and advantage” in violation of the

State antidiscrimination laws. 46

Several utility commissions have already

authorized programs to finance the installation of insulation to conserve natural gas. 47

Since it can be reasonably claimed that conservation by some consumers contributes to

the eventual economic benefit of all, earlier

precedent in support of promotional practices should be applicable. Some States

Environmental Concern. Structural Change In the

Process of Public Utillty Price Regulation, ” )ourna/ of

Law and Economics 17(1 974): 291

4’ Lefkowitz v. Public Serv. Comm’n, NO 593 [N. Y.

Ct. App., Dec. 28, 1976), affg 377 N Y S 2d 671, 50

App Div. 2d 338 (Sup. Ct. 1975).

4’ 377 N.Y S 2d at 674

47 E g , Re Pacific Power & Light Co , Case No

U-1046-29, Order No 8567, 69 P U R 3d 367 (Idaho

Pub Ut{l Comm’n 1967), In the Matter of the Appllcatlon of Mlchlgan Consol Gas Co for Authorization of

a Program for the Conservation of Natural Gas, 1

P U R 4th 229 (Mlch Pub Utll Comm’n 1973 )

Related decisions by publlc utility commissions have

allowed the restriction of energy to approved uses

and the prohlbltlon of energy use by uses considered

wastef u I.
190 ● Solar Technology to Today’s Energy Needs

have adopted legislation specifically authorizing conservation programs, eliminating any doubt about their validity.48

If rate structures that encourage conservation are valid and mandated, subsidies for

use of solar energy, which employ a nondepletable, nonpolIuting energy source,

should also be valid. Use of solar energy is

supported by the same public interest and

public policy as conservation–decreased

use of fossiI fuels.

State antidiscrimination statutes are not

the only factor to consider in d incriminatory

practices by utilities. The Federal antitrust

laws may also outlaw rates or services that

single out the owners of solar energy systems for special treatment. The longstanding antitrust exemption for State action will

not totally immunize public utilities from

antitrust Iiability.49

There are several grounds on which utility

rate and service discrimination toward solar

users could be deemed anticompetitive, and

therefore a violation of antitrust laws. A

utility may be deemed a monopoly if it

charges a very high price or even refuses to

provide backup service to solar customers. 50

An antitrust violation might also be found if

a utility subsidizes its entrance into the solar

heating and cooling market by distributing

its losses across all utility customers, giving

it an overwhelming advantage. 5

‘

48 Cal Pub Utll Code $325007, 2781-88 (West); N J

Stat Ann ~~ 482-4823 (West)

49 In Cantor v Detroit Edison Co., 96 S Ct 3110

(1 976), the Supreme Court said that a privately owned

publ IC utll Ity IS not exempt from possible antitrust

Iiablllty when It furnl~hes Its customers with Ilght

bulbs tree ot charge, even though the Ilght bulb promotional practice had been approved (as part of the

ut I I Ity’s rate structure) by the State public ut I I Ity com -

m Isslon

50 Refusa/s to deal area classic kiolatlon of section 2

of the Sherman A c?, 15 U. S C. $2 (Supp IV 1974) See,

e g , Otter Tall Power Co. v United States, 410 U S 366

(1972), where a publlc utlllty wds found to have vloIated section 2 of the Shermdn Act by refusing to sell

electricity to a municipally operated distribution

syJtem

The conference committee on the National Energy Act has, at this writing, taken

steps toward resolving these rate issues, but

failed to completely clarify the situation.

While most of the President’s proposals for

dictating rate reform at the Federal level

failed to gain conference approval, the conferees did allow the Federal Energy Regulatory Commission (FERC) to prescribe rules

requiring electric utilities to offer to sell

power to or to buy power from qualifying

cogenerators or small power producers and

prevent discrimination against such producers. (Small power producers in this case

are facilities generating less than 8 0

megawatts from sol id waste or renewable

resources; the definition of a qualifying

generator is left to the FERC. ) While this provision permits Federal regulation of the relationship between utilities and small solar

generating facilities, it leaves the difficult

problem of determining just rates up to the

FERC.

ARE ONSITE SOLAR SYSTEMS SUBJECT

TO REGULATION AS PUBLIC UTILITIES?

If an onsite solar system is found to be a

public utility, it must file reports and accounts, 52 serve all customers who demand

service within a given area, submit its rate

schedules to the utility commission for approval,

53 continue providing service until

given permission to discontinue, 54 provide

safe and adequate service, 55 comply with

‘) Such conduct could be viewed as temporary

price-cutting to put rival solar firms out of business.

See Puerto Rican American Tobacco Co. v American

[obacco Co., 30 F 2d 234 (2d Clr 1929) Or, It ml~ht

be viewed as an Illegal tying arran~ement In situations

where a solar customer’s receipt of favorable treatment IS conditioned on hls acceptance of the utillty

service Tying arrangements are another classic antitrust violation See 15 U S C. $ 14 (1 970), /rrterrrational Busines$ Machine Corp. v United States, 298

U S 131 (1936)

“ E g , Fla Stat Ann $366 06(1) (West)

‘) E g , Cal Pub Utll Code 454 (West)

54 E g , WIS Stat Ann 19681 (West)

‘

5 E g., Cal Pub Utll Code 761 (West)
Ch. VI Lega/ Aspects of Onsite So/ar Facilities ● 191

limitations on the issuance of securities, ”

and apply for certificates of public conve -

nience and necessity. State utility reguIatory

statutes universally require that every public utility obtain a certificate before beginning operation or even construction of its

equipment. 5

7

Meeting these requirements would be a

prohibitive burden for most potential owners of solar equipment, since the proceedings are frequently long and expensive, Even

if a solar owner were wilIing to undertake

the trouble and expense to file as a utility,

he would have to recognize that an existing

utility will be able to maintain a monopoly

in its geographical area unless the courts

determine that public convenience and necessity require otherwise

A new utility is therefore rarely permitted

in an area already served by an existing utility. Even where the existing utility is providing woefully inadequate and inefficient

service, it wi I be permitted to exercise

monopoly control over its service area if it

promises to correct its shortcomings.

The initial factor in determination of

whether an onsite solar system is a public

utility is who owns the system? Ownership

can range from the privately owned solar

system on a privately owned residence, t o

cooperatively owned systems for a small

community, to a corporate-owned colIector

field on corporately leased or publicly

owned property to utiIity-owned systems on

private residences. Clearly, somewhere in

the continuum of owners the onsite solar

facility and its owners became subject to

reguIation as a public utiIity.

“ E g , [id Stat Ann ]66 O-I (West)

“ ‘ E g , I I I t?E’V Stat , ch 1112 3, 56

‘“ See, e g , KentucA y Ut/i C 0, v Pub/Ic $erv Comm n, 252 S W 2d 885 (Ky )

5 ’ f g , F la Stat Ann $ 36601, Mlch Comp 1 aws

Ann $460-6, Cal Pub Utll Code ~ 21 6(a)

‘“ WI\ Stat Ann $19601 (West), Ill Rev Stat ch

111 2 ; Q 10, e g , A //en v California R /? Comm ‘n, 179

Cal 68, 175 p 466(1918)

Ownership

Most State statutes define a public utility

to include any person, corporation, partnership, association, or other legal entity and

their various representatives.59 A solar faciIity owned by a landlord, or a private property owner, as well as any partnership or corporate entity would qualify as a public utility, if the other qualifications are met,

Where there is no sale of electric power

involved, but rather the owner and user are

the same legal entity, State regulations govern. Federal regulations concern only the

wholesale rate for interstate electricity

sales, Rarely will owner-used energy be subject to Federal regulation as a public utility.

This is true whether the owner is a single

family, a joint venture composed of the various users, or a corporation which supplies

its own corporate needs.

Where the owner is not the sole user,

State statutes vary, The general rule is that a

company which supplies energy “to the public” will be found to be a public utility,

whereas a device which is not producing

energy for public use will escape utility

reguIat ions, 60 Law in this area is very unclear

and the ambiguity may be a barrier to the introduction of solar equipment,

A facility can be judged to be dedicated

to “public use” if its owners 1 ) demonstrate

a wiIIingness to serve alI who request service;

61 2) voluntarily submit to State regulation; or 3) attempt to exercise the power of

eminent domain.62 

‘1 “The principal determinative charactlstlc of a

public uti i Ity is that of service to, or read lnes~ to ierve

an Indefinite public which ha~ a legal right to demand and receive its services or corn mod I t I es ‘‘Motor

Cargo, /nc. v. Boarcf of ~own.~hlp Trustee\, 5.2 Ohi o

Op 257, 258, 117 N E 2d 224, 226 (C P Summit County

19’52) See gerrera))y A J C Prle$t, “Some [J~ses of

Publlc Utility Regulation, ” MIssI~sIppi Law journa/ 36

[1965) 18 See, e g , Peoples Gas Light & Coke Co v

Ame$, 359 I I I 132, 134 N [ 2W (19 35), Story v

F?icharc]son, 186 Cal 162, 198 p 1057 (1921)

“ See Dow Chemical Co , et al , Energy Industrial

Center Study, p 373 and cases cited therein
192 ● Solar Technology to Today’s Energy Needs

Even activities which do not clearly involve a dedication to public use may be declared by the courts to be “so affected with

the public interest” that utility commission

jurisdiction is justified. In one recent case,

the owner of a shopping center was not

allowed to sell energy to stores in the shopping center without being regulated as a

ut i I ity. 63

Electricity, Steam, or Heat?

Another factor in determining whether an

onsite solar use is subject to regulation as a

public utility is the form in which energy is

supplied to the users —electricity, thermal

energy (steam or hot water), or chemical

energy. Solar equipment may become available which will produce energy in each of

these forms. Again, State statutes vary, For

example, some States do not vest jurisdiction over production and sale of steam in

their utility commission.

64 State statutes

vary greatly, however, and generalIy thermal

energy is not regulated simply because there

is no explicit mention of the issue in the

statutes,

Still another aspect of this question is

whether the sale of energy by an onsite producer subjects the owner of the onsite

equipment to regulation. Sale to a presently

regulated utility should be interpreted as

would sale to any other category of user.

Under most State statutes, sale of excess

steam or electricity to a specified public

utility probably would not meet the test of

dedication to public use which is required in

determination of public utility status. In a

number of cases, industries that generate excess electricity or steam or selI it to public

utility companies have been held not to be

public utilities.65 However, in some States

the opposite has resulted.

The congressional revision of the National Energy Act takes some action in ex-

‘ i Cottonwood Mall Shopping Center, inc. v Utah

Power & Light Co., 440 F 2d 36 (lOth Clr 1971).

‘4 Mlch Comp Laws Ann $460501, Fla Stat Ann.

Ej 36602

‘5 See Dow Chemical Co , et al., op. cit., pp.

374-376, and cases cited therein

empting onsite owners from regulation, but

leaves many issues unresolved. The conference agreed to exempt cogenerators and

small powerplants producing up to 30 megawatts of electric power from State utility

regulations (apparently granting the FERC

the authority to overrule States in these

issues) and exempts biomass generators

smaller than 80 megawatts from the Public

Utilities Holding Act. The act would, however, apparently not permit exemptions for

subsidiaries of utilities since small generators qualifying for the exemption must be

owned by organizations whose primary business is not energy generation,

CAN A UTILITY OWN

AN ONSITE SOLAR FACILITY?

The above discussion has assumed that

the owner of the onsite solar system was

also the owner of the land and building

upon which the solar system is located. Is it

permissible for utilities or other corporations to own onsite solar facilities on Iand

which the utility does not own, such as the

property of the user?

The short answer to this question seems to

be yes, although antitrust laws and State

policies designed to promote competition

would probably prevent utilities from establishing exclusive marketing rights for solar

equipment. Utilities probably would be required under existing law to compete with

other distributors of solar systems.

The law is clear that utilities at least

would not be barred from the solar equipment market. A recent analysis of the question of permitting gas utilities to invest in

onsite conservation equipment concluded

that Federal antitrust statutes would not be

violated if the utility only purchased conservation devices (in this case, insulation material) from independent suppliers and did

not actually manufacture or install a major

share. 66 

“ Willlam G Rosenberg, “Conservation investments by Gas Utilities as Gas Supply Option, ” Public

Utilities Fortnight/y, Jan 20, 1977, pp 19-20
Ch. VI Legal Aspects of Onsite So/ar Facilities ● 193

Exemption from Federal antitrust statutes

is apparently permitted in some cases where

an expansion of utiIity operations is undertaken at the suggestion of a State utility

commission and not on a utility’s initiative. 67 Precedents exist permitting utilities

both to expand their business to include activities under regulatory authority and to

own subsidiaries which are not reguIated.

There have been cases where, at a utility’s

request, an unregulated industry was placed

u rider reguIatory control. The Pacifi c

Telephone Co., in California, for example,

owned an unregulated subsidiary for a number of years which installed and operated

mobile radio telephones. The company subsequently asked the California Public Utility

Commission (PUC) to place this activity

under regulatory control. The PUC accepted

the application, but a private competitor appealed the decision. The California Supreme

Court upheld the PUC approval, in a divided

decision. The court found that mobile telephone service was closely related to the

utility’s regulated business and that the

equipment, used for telephone communication, fell under the jurisdiction of th e

reguIatory authority. 68

At the same time, there are cases where

utilities have not been able to place subsidiaries of this type under PUC reguIation.

For example, the New York Service Commission limited the activites of utilities in solid

waste disposal ventures,

69 and AT&T wa s

prohibited from expanding its unregulated

business as a part of a settlement.’”

b’ Cantor v Detro/t Edison Co., 96 Sup Ct 3110

(1 976)

“ Corrrrnerc/a/ Comrnunicat/orrr /nc v Californi a

Pub/Ic Uti//ty Cornrn/ssion, 50 Cal 2d 512 (1958)

“ P M Meler and T H McCoy, So/Ic/ Waste as an

Energy Source for the Northeast, prepared for the

Energy Research and Development Admlnlstratlon

(Upton, N Y Brook haven National Laboratory, No

50550, 1976], p 96

“) Un/tecf S?ate$ v W’estern E/ectr/c and AT&T, 13

Rad Reg (P-H) $2143, 1956 Trade Reg Rep (CCH)

571,13-4 (D N J 1956) (consent judgment)

It is unclear whether an existing public

utility wiII be permitted to own a solar

system which is permanently placed on the

roof or other property of a customer. Since

such a system is probably a fixture, the utiIity would be required to leave the solar system in the home or office, even if the property is sold or leased. The most practical approach is for the utility to finance the purchase of the solar equipment and thus perm it its easy disposition as a fixture, but retain the usual metering, repair, and maintenance relationships with the customer.

Nonutility corporations could also own

onsite solar equipment. Probably, such a

corporation would supply only equipment,

and perhaps maintenance, but not energy.

Under most State statutes, provision o f

energy equipment is not subject to utility

commission jurisdiction.

The specific arrangement between the

solar equipment leasing company or seller

and the property owner may alter the question of utility regulation. For example, the

inclusion of a service agreement between

the lessor and the lessee might increase the

likelihood of regulation, as would mor e

widespread adoption of solar devices. AdditionalIy, to the extent that such an agreement requires backup power from public

utilities, the contracts and prices for these

provisions would be indirectly subject to

regulation as part of the normal utiIity rate

reguIation.

Congress apparently has taken a dim view

of utility ownership and financing, since the

committee of conference on the National

Energy Act rejected the President’s proposal

that utilities be permitted to finance the instalIation of insulation and other expensive

residential conservation equipment. While

the conference encourages utilities to perform energy audits of residences, it prohibits

utiIities from instalIing conservation devices

other than furnace-efficiency modification,

clock thermostats, and load-management

equipment. Loans to cover these devices are

Iimited to $300. (State commissions are per-
194 ● Solar Technology to Today’s Energy Needs

mitted to ask for an exemption from this

prohibit i on.)

The field remains quite ambiguous, however, and many possibilities remain open. It

may be attractive, for example, for utilities

to operate solar equipment as a part of an

unreguIated subsidiary. Such an arrangement would eliminate concerns, expressed

by some potential owners of cogeneration

equipment, that equipment on their premises, owned by a regulated utility, would not

be able to sell energy on an equitable basis

because of special pressure to adjust utility

rates.

Municipal Utilities

Since municipal utilities can financ e

plants with relatively low-interest, tax-free

bonds, the capital costs associated with

plants owned by municipal can be lower

than those of plants owned by privately

owned utilities. Lowering capital costs is

particularly important in the case of solar

energy systems where the bulk of the energy

cost results from the cost of capital. I n most

States, however, municipal utilities are prohibited from expending funds for “private

benefit” and this has been interpreted to

mean that municipal utiIities cannot purchase shares in generating facilities which

are partly financed and operated by a

private utility.

These prohibitions may also prevent municipal from owning or operating onsit e

generating systems. In the case of solar

devices, however, it would seem that the

municipal couId make a strong case that installation of a solar device would benefit

the public at large even though it was primariIy designed to meet the energy needs of

a single building. In fact, several municipal

utilities have experimented with onsite solar

energy equipment in their districts. The legal

point may be moot since, as one analyst put

it, “Who’s going to complain?”

In any event, the laws preventing municipal from owning part shares in generating

facilities which will be partly owned and

operated by private utilities are bein g

changed in many areas of the country to

allow municipal to share the cost of constructing nuclear-generati ng facilities and

other centralized energy equipment, which,

like solar energy systems, have high capital

costs. Prohibitions aganist such “joint action” programs are often written into State

constitutions. The constitution of the State

of North Carolina, for example, was recently

amended by referendum to permit jointaction financing of new electric utilit y

plants, Such amendments have been controversial in some areas. For example, in 1977,

the Governor of Indiana vetoed legislation

amending that State’s constitution to allow

joint action programs.

Cost-Sharing Issues

If a utility were to own or operate onsite

generating facilities, contracts between customers and the utiIity wouId have to address

several important issues. They include:

●

●

●

●

●

●

Who would pay the property tax on the

equipment? (This is particuIarly important because utility tax rates often are

several times higher than those fo r

homeowners.)

How would costs of insurance be distributed? Would utilities be liable for

damage to onsite equipment caused by

the homeowner?

Would a contract for onsite sola r

equipment be binding on a new owner

if title to a buiIding were transferred?

How far would a utility’s maintenance

responsibility extend? Would a utility,

for example, be responsible for keeping

a roof on which a solar collector was

mounted in weatherproof condition?

Should a utility pay a customer for the

use of a roof or wall for installing a

solar collector? If so, would the fee

decrease for the use of walls and roofs

that did not permit optimum collection

of radiation?

Could a customer demand that a utility

remove onsite equipment? If so, who

wouId pay for removal?
Ch. VI Legal Aspects of Onsite Solar Facilities . 195

None of these questions pose insoluble

problems, but all may require careful negotiation. All of the utilities interviewed by the

General Electric Co. said they preferred onsite facilities on large buildings, because

questions would be easier to resolve than if

large numbers of small buildings were involved. 7

‘

WHAT RIGHTS WILL UTILITIES HAVE TO

AQUIFERS AND OTHER GEOLOGICAL

FORMATIONS USED FOR

THERMAL STORAGE?

Several techniques for storing larg e

amounts of thermal energy in ground water

71 General E Iectrlc Corp , Corrceputal Design and

Systems Ana/ys/s of fhotovol?a~c Power Systems, April

1977, ERDA contract E(ll-1 ) 2744, op cit

and in heated underground caverns have

been proposed (see chapter Xl), and the use

of subsurface regions for such purposes may

raise a number of difficult legal questions.

For example:

Would a utility need to purchase mineral rights to use subsurface water or rock

for thermal storage?

What aspects of water laws govern

which aquifers can be used, the contamination permitted, the heating of

aquifers which might be used for potable water, etc. ?

Would the owner of heated water have

protection from someone tapping this

hot water supply?

What environmental laws would apply

to large-scale thermal storage?
Chapter Vll

THE IMPACT OF SOLAR ENERGY ON

U.S. FOREIGN POLICY, LABOR, AND

ENVIRONMENTAL QUALITY
Chapter VII-THE IMPACT OF SOLAR ENERGY ON

U.S. FOREIGN POLICY, LABOR, AND ENVIRONMENTAL QUALITY

Page

Background ... *.. **. **. . ... .* s.*.... 199

Developing Nations. . . . .................202

Implications for U.S. Policy . .............203

Foreign Trade in Solar TechnoIogies ........208

Background . . . . . ......................208

Foreign Competition in Solar

Technologies. . . . ....................209

The lmpact of SolarEnergy on

American Labor... .. ...................210

ManpowerRequirements. . ..............210

SomeQualitativeImpacts . ..............213

Long-TermImpacts. . ...................218

Net Energy Use of SoIarEquipment ... ......219

Primary Energy Requirements . ...........219

Energy UsePerDollarofGNP . ...........220

Thelmpact of On$iteEnergy on the

Environment . . . . . . . . . . . . . . . . . . . . . . . . . . .222

Direct Environmental Effects. . ...........222

OnsiteSolarEnergySystems and

Land Use. . . . . . . . ....................225

TheAdverse Environmental Effects of

CollectorFields. . . ...................231

Land Used by Conventional Generating

Systems . . . . . . . . . . ..................231

lmpact on BulldingDeslgns. .. .............232

Background . . . . . ......................232

Roof Pitch and Orientation. . .............236

Space for Storage . .....................237

Other Building Impacts. . ................241

LIST OF TABLES

TableNo. Page

l. Electricity Prices in Developing Nations ..205

2. Labor Requirements for a Conventional

800 MWe Coal Plant... . ................211

3. LaborRequirements of TwoTypes of

DistributedSolarEnergySystems. . ......212

4. Skills Required for Constructing a CoalFired Electric Generating PlantandOper-

 ating the System Over a 30-Year Period ...215

5. Detailed Breakdown of Skills Required

for Conventional ElectricSystem . .......216

6. Energy PaybackRelations for Onsite

SolarConversionSystems in Albuquerque 220

7. MaterialsRequired in Solar Energy

Devices(kg/ m

2

) .. .....................221

TableNo. Page

8. Primary EnergyRequired to Produce

ComponentMaterials for Solarand

Conventional PowerSystems . ..........221

9. EmissionsAssociatedWith the Energy

Requirements of a Single Family House

in Omaha, Nebr.. . .....................224

10. Primary EmissionsAssociated With

Energy ResourcesAvailable for

Residential Commercial and Industrial

Consumers . . . . . . .....................226

“PaybackTime’’ for the Emissions

AssociatedWith the Manufacture of

Solar EnergySystems. . ................226

Land Required for Strip-Mining Coal. ... .231

PotentialAreasfor Collectors on Typical

Buildings . ...........................235

Thermal and Electric Outputs of

Flat-PlateCollectors in Omaha, Nebrv

as a Function of Tilt Angles and

Orientation . . . . . . .....................240

LIST OF FIGURES

Figure No. Page

l. Worid EnergySupply and Demand . ......200

2. WorldwideAvailability of Sunliaht

3

4

5

Resources . . . . . . . . . . . . . . . . ._. ... ... ...2O4

A Small Housing Development Using

Solar-Heating Devices . ................228

Tracking Collectors Mounted Over

a Parking Lot . ........................229

VegetationGrowing UnderArrays of

SolarCollectors. . .....................230

6. Techniques for lntegrating Solar

Collectors Into Conventional Designs

for Single Family Residences . ..........233

7. Techniques for lntegrating Solar

Collectors Into Conventional Designs for

Townhouses and LowRiseApartments ...234

8. Presidential BuildingWith Optimized

SolarRoof Pitch and Orientation. . .......236

9. A Commercial Building Designed To

Optimize Roof Pitch and Orientation .. ...237

10. A Proposed installation for a OneAxisTracking Collector . ...............238

11. Use of Collectorson the Vertical

Wall of a High Rise Hotel . ..............239
Chapter VII

The Impact of Solar Energy on U.S. Foreign

Policy, Labor, and Environmental Quality

BACKGROUND

Extensive use of solar energy throughout the world would relieve some

of the international stress which results from competition over diminishing

energy resources. Solar energy is one of the few energy resources reliably

available throughout the world and, to the extent that it can be developed in

lieu of conventional energy sources, it can reduce the uncertainties and trade

imbalances which have resulted from energy imports.

Moreover, solar energy technology can be implemented without the

technical infrastructure and cadres of skilled engineers required to implement most other energy strategies— in developing countries solar energy

may provide a technique for converting low-cost labor into low-cost energy.

While it is difficult to anticipate how fast solar energy will be introduced into

the world energy market, it appears that solar energy’s impact is likely to be

quite small in the next few decades unless accelerated programs for developing this industry are undertaken.

It is likely that solar energy will grow more rapidly abroad than it does in

the United States, since U.S. energy prices are relatively low, U.S. domestic

energy supplies are relatively large, and U.S. labor costs are relatively high.

However, U.S. policy in solar energy will probably play a critical role in influencing the development of this technology throughout the world: the

United States now probably leads the world in the quality of its solar

engineering. The United States can influence utilization of solar energy in

developing countries through its economic assistance programs and a major

U.S. commitment to the use of solar energy for its own use would give a

prestige to the field which may attract worldwide emulation. The history of

the past two decades clearly indicates that these three effects resulted in a

rapid transfer abroad of U.S. interest i n fission reactors.

The eventual need to develop renewable

sources of energy is beyond serious contention, although there is disagreement about

the urgency involved. There are two parts of

the problem: near-term depletion of lowcost oiI and gas reserves, and the depletion

of all fossil and uranium resources over the

long term.

Many recent studies have indicated that

world demand for oiI and gas may exceed

supplies by the middIe of the 1980’s, 2 I n the

past two decades most of the developed nations of the world and the industrialized sections of developing nations have become

heavily dependent on the convenience and

low cost of petroleum and natural gas, and

consumption rates have become astro -

nomical.

A shortage of indigenous supplies of these

fuels has required many nations to import

them and in many cases, dependence on

these imports is heavy. This dependence is

likely to increase during the next decade

because of the shortage of acceptable alternatives, and the high costs and long construction times needed to convert to the

alternatives which become available. The

uncertainties associated with importing a

199
200 ● Solal Technology to Today’s Energy Needs

large fraction of a critical material are

amplified by the fact that world resources of

petroleum are inequitably distributed. The

OPEC cartel, for example, controls 68 percent of known world reserves of o i 1, and its

Middle Eastern members alone control 55

percent of known reserves.

Coal and other fuels can be substituted

for oil and gas even though the use of these

energy sources is not as convenient as liquid

‘ ()// ,)nd (;,]J /o(/rn,q/, De(- 29, 1‘)75

Area

Africa

Asia (less U. S. S. R.)

Europe (less U S S. R.)

U.S.S.R.

North America

South America

Oceania

Total

fuels. The use of coal resources may be

limited by environmental problems, transportation costs , and other difficulties .

Figure VI l-l indicates that if world energy

consumption grows at its current rate, proven world reserves wiII be entirely consumed by 2015, If the entire world consumed

energy at U.S. consumption rates, world

reserves would be depleted by the end of

this century, It is, of course, unlikely that

production or consumption rates will continue to grow exponentialIy and new energy

sources, such as fusion, may be available to

Figure VI I-1 .—World Energy Supply and Demand

Measured World Recoverable Energy Reserves, 1974

Solid

fuels

361.7

2.608.7

2,581,5

3,325.5

5,070.9

49.8

459,8

14.457.9

I Quadrillion Btu]

Crude

oil

526.6

2,202.4

57.1

333.6

301.0

311.5

9.4

3,741.2

Natural

gas

201.7

432.6

153.6

577.9

380.6

60.6

24.9

1,831.9

Oil shale

and

tar sands

81.4

8702

117.0

139.0

9,111.0

23.7

9.2

10,3515

Uranium

(nonbreeder) 2

1981

3.1

46.4

Unknown

422.7

11,9

99.1

781.3

Total

1,369.5

6,1260

2,955,6

4,376.0

15,286,2

4575

602.4

’31 ,1732

‘ Accordlrw to the U S De~artment of the Interior Bureau of Mines North Amer)can tar sands and shale 011 reserves may be severely

overstate: Development of most of these reserves IS not econom IC at present

‘ Enerqy content using breeders 60-100 t)mes as great Thortum resources neglected

SOURCE World Energy Conference Survey of Energy Resources New York 1974

World Energy Consumption, Production, and Inventory Changes

260 

“ 100

80

60

gas consumption

Petroleum consumption

SOURCE Energy Perspectives 2 U S Department of the Interior, June 1976 pp 11 and 20
provide essentially inexhaustible supplies of

energy in the next 20 years, but it is difficult

to take great comfort from the available

statistics.

World supplies of fuels other than oil and

gas are also inequitably distributed Figure

VI l--i indicates that nearly half of known

world energy resources are located In North

America (although the share would be reduced somewhat If oil shale assets are

overstated) The United States, U S S R , and

Eastern Europe control 73 percent of the

known world reserves of coal 4 

.

There can be Iittle doubt that growing

uncertainties about energy supplies wil l

have an Important Impact on international

political stability during the next decade intensive efforts will be made to develop

domestic resources and to ensure the security and reliabllity of foreign supplies The latter objective, however, would appear to be

Increasingly difficult to achieve The effort

to assure supplies and the vast transfers of

assets between nations which occur in the

process, can create economic dislocatlons

in developed nations and frustrate th e

aspirations of less developed nations This,

In turn, could lead to restructuring of world

alIiances There has been specuIation, for

example, that democratic institutions (in nations such as Italy) may collapse under the

weight of accelerating Inflation and recession traceable, at least in part, to energy

costs Dr Henry Kissinger has warned that:

Not since the 1930’s has the economic

system of the world faced such a test. The

disruptions of the 011 price rises, the threat

of global InfIatlon, the cycle of contraction

of exports and protectionist restrictions, the

massive shift In the world’s financial flows

and the Iikely concentration of invested

surplus 011 revenue In a few countries, al I

threaten to smother the once-proud dreams

of universal progress with stagnation and

despair

The sense of insecurity attached to importing energy resources is magnified by the

fact that in most cases supply lines for

4 Wilson, p 171

2,{ - ‘i *.? I ) - 14

energy are very long and thus potentially

very vulnerable No nation can be comfortable if a commodity on which Its economy

depends comes from so uncertain a source

Moreover, in any situation where a state or a

group of states greatly dependent on Imports can assemble a substantial military

ca pa b i I i t y, a disruption , or threatene d

disruption, of those supplies carries with It a

high risk of International violence It I S

noteworthy that the U S response to the embargo of 1973-74 included thinly veiled

threats of military action

Another potential source of energy -

related conflict concerns nuclear proliferation The global spread of civilian nuclear

energy has been accompanied by a decline

in the number of technological, economic,

and time barriers to acquiring nuclea r

weapons An increasing number of countries

are already capable of producing their own

nuclear arms The consequences of proliferation are subject to debate, but they are

unlikely to be positive from the perspective

of U S or global interests. A strong argument can be made that proliferation wil l

jeopardize regional and global stability, increase the Iikelihood of nuclear war, exacerbate the threat of nuclear-armed, nonstate

terrorism, and greatly complicate U S. relations with new (potential or actual) nuclear

weapons states. Because securlty concerns

are a key incentive to acquiring nuclear

weapons, the probability of prolIferation

will tend to be greatest in regions with the

highest potential for international conflict

In the past, the United States placed major emphasis on aiding nuclear energ y

development programs around the world In

recent years, this progra m has bee n

tempered by a concern about proliferation,

resu I t i ng in efforts to tighte n export

agreements, to prohibit the export o f

facilities for reprocessing plutonium o r

enriching u ran i u m, and to discourag e

foreign transfers of such technology.

The United States, however, is in a weak

position if it attempts to discourage the development of nuclear power in nation s
202 Ž Solar Technology to Today’s Energy Needs

where attractive alternatives are not

ava i I able.

DEVELOPING NATIONS

Less developed nations are likely to be

most vulnerable to energy shortages and a

steep increase in energy prices. They will be

less able to compete for scarce resources

and less able to bear the additional financial

burdens. (It could be argued that less developed nations wilI fare better than developed

nations, since the less developed a nation is,

the easier it will be to return to noncommercial fuels such as dung and wood ) Plans for

developing an indigenous industrial base

and modernizing agricultural methods have

already been disrupted by higher energy

prices. Many irrigation systems in South

Asia, for example, stand idle because the

fuels to operate them cannot be obtained.

The economic assistance programs of the

developed nations are partly responsible for

the dilemma. These programs have in many

cases attempted to promote the development of an industrial infrastructure which is

as heavily dependent on scarce energy

resources as U.S. industries.

The relatively small onsite solar technologies examined in this report should be

particuIarly attractive to developing nations

for a variety of reasons:

●

●

These nations typically have not invested in an extensive network o f

transmission and distribution facilities

(equipment which frequently costs as

much a s the generatin g stat ions

themselves); onsite technologies could

provide power to dispersed site s

withou t the expens e and dela y

associated with building such equipment.

Onsite equipment does not require an

enormous investment of capital in a

single project, thereby reducing the

overall risk of the investment an d

avoiding expensive capita I-carrying

charges during construction.

●

●

●

panded flexibly and proportionately to

meet growing requirements for energy.

Large facilities produce sudden large

increments in capacity which are difficult to manag e This problem frequently results in prolonged periods of

expensive overcapacity

Some of these advantages would be reduced or eliminated if it were necessary to

construct a centralized utiilty large enough

to meet all energy requirements of the area

under the assumption that solar equipment

might supply no energy during some period

of peak demands There are a number of

ways of eliminating the need for centralized

backup power in developing countries:

●

●

●

The facilities requiring energy could

s i m ply be shut down when energy was

not avaiIable — this would reduce labor

productivity but would not be as significant in a Iocation where Iabor was relatively inexpensive

Many solar applications, such as water

pump i n g, will need no backup in remote areas since storage is very inexpensive

SmalI emergency generating equipment

could be maintained to provide backup

power when solar energy fails. Energy

from diesel generators is commonly

used in remote villages and is very expensive, but the costs would be more

manageable if the devices were only

operated a few days each year
Ch VII Impacts of Solar Energy ● 2 0 3

Solar energy should also be attractive to

the less developed countries on grounds of

broad social utilitv

As a relatively labor-intensive means of

power generation (both in terms o f

manufacture of components and installation), solar energy should help alleviate the endemic high unemployment

and underemploymen t that plagu e

most developing countrles

Village siting of solar facilities would

help raise rural living standards This

could, in turn, have the effect of reducing the rate of migration to urban areas

in search of employment which is often

available only in urban areas because

only urban areas have adequate supplies of energy

Solar energy facilities can be con -

structed utilizing a variety of materials,

which may be 

locally available.

Developing solar energy would no t

commit those countries to forms o f

energy production that they may not be

able to sustain because of fuel shortages or the lack of secure funds for

operating costs

Solar energy may well become economically attractive in developing nations In

many applicat[ons significantly before it

does so in the United States for a number of

reasons Most developing nations are located in areas where sunlight is plentiful

(see figure VII-Z); labor costs–which frequently represent a substantial fraction of

the total costs of a solar energy installation — are relatively low; and the cost of

competing energy — when it is available— is

frequently ver y high. Table VI I-1 summ a r izes the prices charged ror ectricity in

many nations around the worId. The in -

formation IS difficult to Interpret since many

governments subsidize the selling price (For

reference, the fuel prices alone contribute

over 3¢/kWh to the cost of electricity If

petroleum is Imported at world 011 prices )

The table does show, however, that energy

prices in many parts of the world are several

IMPLICATIONS FOR U.S. POLICY
204 Ž Solar Technology to Today’s Energy Needs

Figure VII-2– Worldwide Availability of Sunlight Resources

Daily Radiation for June

Daily Radiation for December

SOURCE John A Duffle and Willlam A Beckman, So/ar Energy Thermal Processes, John Wiley& Sons, New York, 1974, pp 35,37
Ch. VII Impacts of Solar Energy ● 2 0 5

Table VII-I. —Electricity Prices in Developing Nations

Electricity prices

(cents / k Whr)

Capital city Urban,

Country Residence Commerce Industry noncapital Remote Comments

Bureau: Asia

Philippines . 1.6-4.7 2.2-4.7 2.8-3.2 3.8-16 Remote: Regional national

grid, 3.8; Private small

COOPS, 16

Pakistan . . . 2.2-2.5

Indonesi a 7

Sri Lanka . 4-2

Nepal . . . . . . . 2-4

2.2-4.2 .4-1.5

10 .5

Bangladesh. 1.1-1,9

India. . . . . . . . 2.8

Afghanistan 1.7-6.6

Subsidized

Different rates for Hydro,

Diesel, Gas

Korea . . . . . . . 4.6-11 3-4

Thailand* . . . .70-5

5.6-7

● BAHT/kWhr

Bureau: Near East

Yemen . . . . . 13.3

Israel . . . 4.3

Egypt . . . . . . 1.4-2.4

4.6-6.6

1-2.4 1.0 Subsidized (e. g., fuel 011

supplied at 1 /6 world price)

Syria . . . . . . 5

Morocco . . . 5.5-13

Portugal . . . . 3

Sudan . . . . . . 8.6

12.5

4 4

Bureau: Latin America

Ecuador, . . . . 1.5-3.8

25/month

for 25 watt

bulb

Haiti . . . . . . 5.5-7.3

1-2.5 3-4

4.4-4.7

Colombia . . . 1-1.2

Costa Rica . 4.4-5.3

Guatemala . 4.4-6.4

4.7-6

Peru . . . . . . . . 1.9

Guyana . . . . . 19-21.9 29.9 27 Bauxite manufacturer gets

subsidized rate of 10
206 ● Solar Technology to Today’s Energy Needs

Table Vll-1.—continued

Electricity prices

(cents/kWhr)

Capital city Urban,

Country Residence Commerce Industry noncapital Remote Comments

Dem. Rep. ● .

Brazil . . . . . . .

Nicaragua . . .

Panama . . . . .

Uruguay. . . . .

Paraguay . . . .

Chile* . . . . . .

Bureau: Africa

Benin . . . . .

Burundi . . . . .

Nigeria. . . . .

Cameroon . . .

Tanzania . . .

Liberia . . . . . .

Niger . . . . . . .

Senegal . . . . .

Chad . . . . . . .

Kenya ., . . . .

Sierra Leone .

Upper Volta.

Mauritania. . .

Ethiopia. . . . .

2-6

5.6

.87-11.3

6-10

4-5

5-8

.68-1

13

5

3-6

19

3-13

6.5-8

10-19

7-24

14-26

2.8

9

16-26

17

5-7.5

2-3

13

5

3-6

19

12-27

6.5-8

10-19

11-25

14-26

11.2 -15.8

9

5-7.5

2-3

6-8

13

5

3-6

—

7-1o

5.5-7

● in RD ($RD?)

6.9 3.7 plus 23% Fed. Tax

should low residence be 8.7?

uniform in country

uniform in country

6-8

1.4 CH $

13

5 Two cities: one hydro, one

(smaller) diesel. Plans for

small hydro for 3 towns

(GEIL)

4-7

23

Heavy Industry, 1-3

Complicated billing

Average for Mission

Residences, 12.5

7-14

Average for Embassy

housing, 2

6-14.2

9

16-26

5-1o 10-12

8*

SOURCE Mew for lnt~rnal(onal o~v~lw~~nt response to telegram requests for Information Summer 1977

related tensions lead to conflict (even if we attempts to improve relations with the Third

were not directly involved in the conflict), World.

and it has already been eroded by our grow- As the world’s largest consumer and im- ing reliance on fragiIe supply routes for

energy supplies critical to our economy. porter of energy and the acknowledge d

leader in most energy technologies, the

Short of open warfare, competition over United States will necessarily be the focus

energy supplies could place a serious stress of international tensions generated b y

on traditional U.S. alliances and disrupt its energy issues. Washington’s relations with
Ch. V// Impacts of So/ar Energy ● 207

other industrialized countries (many of them

U.S. allies) have already been strained by efforts to impose controls on nuclear exports

and by a competitive scramble, following

the 1973-74 embargo, to obtain reliable

sources of oil imports. With the emergence

of the United States as a major importer,

petroleum has become a potentially serious

source of division within the Atlanti c

Alliance, and with Japan. By contrast, Soviet

capabilities to export oil and uranium have

augmented the U.S.S.R.’s hold over its

clients in Eastern Europe.

Its wealth and power have long made

America the representative and symbol of

the industrialized state in the eyes of less

developed countries. Thus, inevitably, the

Unitd States has been the focus of Third

World resentment, a condition exacerbated

by the scale of U.S. energy consumption in

an increasingly shortage-conscious world

and by recent American efforts to constrain

nuclear exports.

A danger exists that energy problems may

serve to reinflame some of the anxieties and

ambitions which formerly dominated relations between the Communist and non -

Communist nations. For example, there has

been fear that the U.S.S.R. may successfully

exploit the Arab-Israeli dispute to obtain influence over the disposition of Middl e

Eastern oil, upon which most of the industrialized countries of the world are so

dependent. Rising energy costs, in conjunction with population, food, and resource

pressures, may also frustrate the development hopes of many Third World countries,

thereby strengthening the hand of Communist movements in those countries and

consequently placing new strains on U. S.-

Chinese relations,

Problems have also been created by the

current administration’s attempts to control

the proliferation of nuclear weapons technology by discouraging non-nuclea r

weapons states from acquiring advanced

nuclear energy equipment such as uranium

enrichment and reprocessing systems. Efforts in this area have been rebuffed for a

number of reasons, but two problems clearly are large factors:

●

●

It

The failure of the United States to be

able to offer any logical alternatives to

the proposed nuclear development programs, and

The implication that advanced nuclear

systems are reserved for advanced nations, particularly those with nuclear

weapons capabilities, while other nations are relegated to “second-choice”

energy alternatives not seriously considered by the United States for its own

use.

is clear that accelerated development

of solar energy and other renewable energy

resources throughout the world wilI not be

able to play a large role in the difficulties

discussed here in the near future. But the

development of a reliable energy source, applicable in a variety of countries, operating

largely independence of foreign supplies of

resources or technology, would certainly

move things in the right direction.

Solar energy offers a particularly promising avenue for improving U.S. relations with

the Third World — an area in which Washington has not been notably successful in recent years— because it is peculiarly adaptable to the needs of the developing countries. Solar energy is particularly attractive

in this regard because it offers a means of

directly contributing to improved well-being

at the village level. Americans have not

been adept at providing technology suited

to the rural conditions, low-skill levels, and

plentiful labor supplies which characterize

the living conditions of much of the world’s

population.

Development of a set of solar energy

systems which were genuinely useful to the

Third World would provide an opportunity

for the United States to demonstrate its concern for the aspirations of developing nations and to reinforce its global reputation

for technological leadership and innovation.

The United States is in a position to

assume leadership in the development of
208 Ž Solar Technology to Today’s Energy Needs

solar energy resources for a variety of

reasons.

In the first place, the United States leads

the world in solar energy technologies. The

U.S. Federal budget in solar energy is probably larger than the combined solar budgets

of the rest of the world. Soviet efforts in

solar energy are virtualIy nonexistent.

Secondly, the United States is in a position to supply capital to developing nations

either directly or through international lending institutions such as the World Bank or

the Export-Import Bank.

Finally, a major U.S. commitment to the

development of solar energy resources both

for its own use and in its economic

assistance policy, would have a subtle but

powerful effect on the attitudes of other nations toward this technology.

FOREIGN TRADE IN SOLAR TECHNOLOGIES

BACKGROUND

If solar energy can, in fact, provide a competitive source of energy in many parts of

the world, the potential for U.S. exporters

should be substantial. There have not been

any systematic surveys undertaken of the extent of this market, either by the U.S.

Government or by U.S. solar industries.

Some observers are convinced that there is a

potential market of many hundreds of million dollars in annual sales to under -

developed nations alone, and see no reason

why the United States cannot capture a

large fraction of that market.

Other analysts are more conservative.

They note the limited capability of poor

countries to finance imports, and the fact

that much solar energy hardware is so simple as to be unprotectable by patent. Moreover, low labor costs in developing countries

and the expense of transporting bulky solar

equipment suggest that many less developed countries will find solar energy an

ideal import-substitution Industry. I t is not

difficult to imagine a nation like Singapore,

which has quickly mastered a variety of

medium-level technologies, developing the

capabilities to fabricate some solar equipment. If this assessment is correct, the U.S.

export market may be limited to relatively

high technology solar components, e.g.,

solar cells, electrical controls, and heat

engines.

More detail is available on photovoltaics

than in other areas of solar technology.

About 113 kW of photovoltaic devices were

sold in non-Communist nations outside the

United States in 1976 (a market of approximately $2 million) and a recent study has

forecast that sales could reach about 88

MW ($44 million) by 1986. 7 This is still much

too small to attract major industrial interest.

These projections will remain speculative

until an overseas solar marketing survey is

conducted to look at the energy needs of

developing countries, the kinds of specialized solar technology that would be required to meet those needs, and th e

capability of the developing countries to

pay for imports or to manufacture their own

equipment, This information would b e

analyzed in the context of existing U.S.

technology, and would indicate both how

extensive the market for off-the-shelf solar

hardware is, and how existing technology

could be adapted to provide the specialized

equipment needed by other countries.

The development of a foreign marke t

woul d also substantially benefit th e

domestic solar energy equipment market,

since the additional overseas demand for

~ Characterization of the Present Worldw/de

Photovo/taics Power Systems Market, the BDM and

Solarex Corporations (Draft report, May 1977).
Ch. VII Impacts of Solar Energy ● 209

solar faciIities would result in larger production runs and more research, This should

reduce domestic prices and accelerate improvements made in devices sold in the

United States, yielding the United States a

long-term advantage, even if developing nations began to produce their own systems in

a decade or so It is likely that foreign

manufacturers would sometimes requir e

U.S. assistance, for example, utilize U.S.,

patents or Iicenses for solar devices,

Estimates of a large potential foreign

market for solar energy are supported by recent studies conducted by the Department

of State. One study, published in November

1976, indicated a substantial potentia l

market for solar technologies in eight oilproducing nations [Algeria, Indonesia, Iran,

Iraq, Mexico, Nigeria, Saudi Arabia, and

Venezuela) The study showed that although

al I eight countries preferred manufacturing

solar equipment themselves rather than importing it, none was making a sufficient

commitment to solar research to produce

equipment which could compete with the

small solar electric-generating equipment

and desalinization processes bein g

developed in the United States. Stat e

Department studies have also indicated that

a smaller but significant market for solar

devices exists in other oil-producing countries and in underdeveloped oil-importing

nations, This last group of countries, according to surveys, was anxious to develop

al I types of non petroleum energy sources

and willing to devote a substantial amount

of their capital if such sources have become

economicalIy and technicalIy feasible. a

Some i nd u st r i a I i z ed count r i es wil l

develop their own solar energy industries

and, as a result, wilI not constitute a significant market for U.S exports The exception

may be certai n high-technology compoents .

8 Mdrtln Prochnik, Of flcc of Nuclear Energy and

Energy Pot ICI(JS, Department of State, private commun I( at Ion, Mdrch 1977

FOREIGN COMPETITION IN

SOLAR TECHNOLOGIES

Significant solar technologies have been

developed in a number of other countries.

Japan, Israel, and Australia produce more

energy from the Sun each year than the

United States, primariIy because they have

used simple hot-water and space-heating

devices for decade s France, Germany,

Japan, and perhaps Israel selI more solar

equipment abroad a n n u a I I y than the U nited

state s

There are several reasons for this. First,

conventional energy in the United States has

been, for the most part, plentiful and inexpensive; consequently, this Nation ha s

delayed emphasis on solar heating and hot

water (excep t in Florida and souther n

California during the 1940’s and 1950’s)

while countries such as Japan, Israel, and

Australia have been installing such devices

for decades, Second, the United States

spends proportionately more for research

than other countries with solar budgets,

most of which stress currently marketable

technologies. Private industry in most other

countries has been more deeply involved in

solar technology than has its U.S. counterpart, and it is private industry, not the

Government, that usually determines an export market. Finally, the United States

spreads its financial resources among a

broad range of solar technologies; many

other countries stress funding of fewe r

specialized projects, which leads to more

rapid marketing of resuIts.

[n the past year, France has doubled its

solar budget to almost $10 million per year,

putting special emphasis on developing 300

kW, 800 kW, and 3.5 MW solar electric systems. West Germany, which spends about $6

mill ion per year, also increased its funding

for solar energy substantially Japan i s

spending about $5 million per year in its

government-sponsored Project Sunshine.

Israel has boosted its solar commitment to

about $2 mill ion. I ran has extended its solar

program, opening a 1 00-person solar institute, Saudi Arabia has created a similar
210 Ž So/ar Techno/ogy to Today’s Energy Needs

center, although smaller, staffed by about

20 technologists. The Common Market has

decided to build a 1 MW central thermal

power station, probably in Italy, and Spain is

in the process of locating a site for a solar

research institute with help from the United

States and several European countries.

THE IMPACT OF SOLAR

ENERGY ON AMERICAN LABOR

Onsite solar technology appears to be

more labor-intensive than contemporar y

techniques for supplying energy; thus, in the

short term, the introduction of solar energy

devices might create jobs in trades now suffering from serious unemployment. I n

general, the new jobs will be distributed

widely across the country and wilI not require laborers to Iive in remote or temporary

construction sites because most workers

should be able to find jobs in areas close to

their homes. Work on solar equipment, for

the most part, should necessitate only simple retraining programs, although there may

be shortages both of engineers and architects qualified to design solar equipment,

and of operators trained in maintenance of

some of the larger and more sophisticated

solar devices which have been proposed.

Assessing the long-term implication of

technological development on the wor k

force, however, cannot be reliably undertake n wit h con temporary economi c

methods. Long-term labor impacts will depend on forecasts of future growth rates

both in the economy and in U.S. energy

consumption — subjects about which there

is grea t confusion and disagreement .

Although making economic projections is

hampered by imprecise methodology, it is

possible at this point to outline some of the

critical issues which concern the effects of

solar energy development on labor.

MANPOWER REQUIREMENTS

One of the most critical issues in

evaluating the impact of a new energ y

technology on labor, and one of the most

difficult to deal with reliably, is how the

technology wiII affect overalI manpower requirements in the energy industry. Tables

VI I-2 and VI I-3 compare the manpower requirements of a conventional coal-fire d

generating system with the manpower required to construct and to operate each of

two kinds of solar devices capable of producing equivalent amounts of energy. Only

first order effects have been considered, and

the estimates made about solar devices are

necessarily speculative. One overalI conclusion seems inescapable, however: a large

fraction of the value of solar equipment is

attributable to direct labor costs.

The high labor intensity of solar equipment is not surprising, Most devices can be

constructed from relatively inexpensiv e

material, and the small equipment examined here would not require extensiv e

capital-carrying charges during construction. Factories for mass production o f

photovoltaic devices, heat engines, and

other components of solar technologies will

probably employ sophisticated and expensive equipment which will reduce labor in

these industries, Much of the work of installing solar equipment wiII continue to require

direct onsite labor.

Table VI I-2 lists all labor requirements for

construction at the plant site, to build the

800 MWe turbine generator in a factory, to

operate the generating faciIity at an average

of 60 per-cent of f u I I capacity for a period of

30 years, to buiId and operate a coal mine

large enough to support the plant, to transport the 2.5 m i I I ion tons of coal per year

needed to operate the pIant, and to construct and maintain a transmission an d
Ch. VIl Impacts of Solar Energy . 211

Table VII-2. —Labor Requirements for a Conventional

800 MWe Coal Plant

(in units of man hours per megawatt year)

. .

Operating

Construction and

maintenance

—

800 MWe coal plant. ... 330 380

coal strip mine using

western coal . . . 20 360

coal preparation plant. 3 290

coal transportation — 340

electric transmissio n 40 5

electrlc dlstribut!o n 190 310

steel & concrete production 10

turbine/generator

manufacturing. . . 170 0

Total . . . . . . . . . . . . . . . . 763 1685

—

Assumptions: — 800 MWe coal plant operating at

peak capacitv for 30 years:

Total

710

380

293

340

45

500

10

170

2348

60 percent

— western’ coal’ strip mine with 525-miIe train line;

— all data based on Bechtel data with the exception of the turbine generator manufacture.

It was assumed that the turbine/generator cost

of $150/kW of which 25 percent was labor and

that this labor was paid at an average rate of

$10/hr;

— calculations divide the sum of construction

manpower and 30 year operating manpower requirements by the total number of megawatt

years of energy produced by the plant.

Table VII-3 presents an estimate of the

labor required to build and maintain a flatplate solar water heating system and a small

tracking photovoltaic system in Albuquerque, N. Mex. The hot water system requires

1.5 to 2.5 times more labor than the conventional coal-fired generating facility and even

more if the utility must maintain a substantial faciIity for providing backup power. The

range shown for the solar devices reflects

the range of labor requirements provided by

collector manufacturers contacted. It I S

probable that the labor requirements of a

mature solar industry will be close to the

lower end of the range shown.
Table VII-3. — Labor Requirements of Two Types of Distributed

Solar Energy Systems

(in man hours per megawatt year)

1. Solar hot water heaters

( 8 m

2 flat plate) . ,

— manufacture collector

—install collector. . . . .

—routine O&M . . . . . . .

Total for hot water system ●

Total for hot water system

including backu p

Il. Tracking silicon

photovoltalc system:

a. Electrlc only (50 m2

)

— manufacture colIector

and cells . . . . . . . . . .

— install collector. . . . .

—operate system. . . . . .

Operating &

Construction maintenance Total

800-2500

1200

—

o

0

1200

800-2500

1200

1200

2000-3700

2340-4040

2600-3300

1800-4600

.

1200

—

—

—

6800

3200-4900

3540-5240

2600-3300

1800-4600

6800

Total for tracking photovoltaic system . . . . . . 4400-7900

Total for tracking photovoltaic system including

backup 4740-8240

b. Electric

+ 0.29-Thermal

(Including backup). . . . . 2240-3740

c. Electric + Thermal

(Including backup). . . . . 1130-1750

6800

—

3000

1240

11200-14700

11540-15040

5240-6740

2370-2990

Assumptions: — 20 year system life;

— installation includes 75 feet of piping costing 0.11

MH/ft to Install;

— flat plates installed for 1.3 MH/m and tracking colIector installed for 1.3-3.33 MH/m2

;

— cells assumed to be 18 percent efficient, optical efficiency 80 percent.

— labor for providing backup power is assumed to be

50% of the construction labor shown in table Vll-2—

(e. g., 340 man-hours/ MW-year)

— flat plates assumed to provide 930 kWh/m2

- y r

(Albuquerque);

cells provide 320 kWh/m2

-yr electric and 1450

kWh/m2

-yr thermal for PV system (Albuquerque);

O&M labor for PV system assumed to be 0.25

hrs/m2

-yr (see table Xl-7);

— flat plate manufacturing labor based on data from

several collector manufacturers;

— concentrator manufacturing labor assumed to be .024

MH/lb of collector for PV concentrator given in table

VII-7 (with concrete and sand excluded) with the labor

to produce the raw materials added;

.024 MH/lb IS approximate labor Input for automobile

manufacturing based on employment and production

for 1973 given in 1976 Sfatisfica/ Abstract of the

United States, U.S. Dept. of Commerce, Bureau of

the Census, pp. 369, 791.
Ch. VIl Impacts of Solar Energy ● 213

Some collector designs (e. g., plastic collectors) will almost certainly require less

manufacturing labor but they will probably

require more maintenance labor, whil e

other designs which require less material

(e.g., tubular designs) may require more

manufacturing labor than simple flat-plate

systems.

The labor requirements per unit of solar

energy delivered would be higher in areas of

the country which do not receive as much

sunshine as Albuquerque since each unit

area of colIector wouId produce less output.

It should also be noted that onsit e

systems which rely on utiIity systems for

backup would probably not reduce th e

labor requirements for transmission and distribution systems significantly. This is important since a large fraction of the labor required by conventional utilities is due to

these energy distribution systems. A shift

toward decentraIized solar energy systems

couId, therefore resuIt in repIacing centralized facilities with solar units requiring

greater amounts of labor while leaving the

labor-intensive distribution systems intact.

SOME QUALITATIVE IMPACTS

While the analysis of the overall labor requirements of solar energy is very primitive,

it is possible to be somewhat more confident about some qualitative aspects of solar

energy’s impact on the work force.

Geographic Distribution

Employment in installation and operation

of solar equipment can be expected to be

distributed over a large part of the country.

Initial installations of solar equipment are

likely to occur in places with high insolation — the South and Southwest, Locations

with relatively low levels of sunlight, such as

the Northeast, however, tend to have high

energy prices, Thus, while low insolation

levels make solar energy in the North expensive, competing energy sources are also expensive, so the net economic competitiveness of solar devices may be as high in the

North as in more favorable climates ,

Employment in installing solar energy is,

therefore, likely to be as geographically dispersed as the building industry.

One thing about solar employment seems

clear— none of the small solar devices considered in this report wilI require the major

dislocation of a work force, or the establishment of temporary work camps as may be

required for construction of a pipeline, an

offshore drilIing operation, or a large central

generating facility in a remote location. The

relatively small solar devices analyzed here

will provide employment in close proximity

to where workers presently Iive, and therefore will avoid the social disruptions associated with large influxes of temporar y

workers.

Unlike most major manufacturi ng

facilities, solar manufacturing at present is

spread across the country in literalIy hundreds of small companies. The future of

these businesses, however, is very uncertain.

If the demand for solar equipment increases

substantially, the field may be dominated by

a small number of large manufacturi ng

firms, much as the manufacturing of conventional heating and cooling equipment is

dominated by a small number of firms.

On the other hand, solar devices may be

designed for special climates and sufficiently site-specific for manufacturing to remain geographically dispersed, much as

facilities for manufacturing modular homes

are today. It seems clear that because of the
214 ● Solar Technology to Today’s Energy Needs

sophisticated technology employed, th e

manufacturing of components such a s

photovoltaic devices, heat engines, and

concentrating devices will occur in a

relatively small number of facilities.

Stability of Labor Demand Associated

With Solar Equipment

If a major demand develops for solar

energy, it is Iikely that employment in the

area will be as stable as work in any typical

building trade; the solar equipment wil l

simply add jobs at each construction site. If

a major retrofit market develops, there

could also be major employment opportunities in this area; maintenance of solar

equipment will also provide a stable source

of jobs.

Skill Levels Required

Most of the employment directly created

by a shift to solar energy will be in installation of the equipment by the conventional

building trades, and in the creation of new

manufacturing industries. The skills re -

quired for installation of the equipment will

be very similar to those required for conventional construction projects, although some

brief training programs will undoubtedly be

desirable to familiarize workers with the

new equipment and its installation. Most of

the work will be in framing roofs, laying

footings, plumbing collectors and storage

tanks, excavating trenches and pits for piperuns and storage tanks, installing sheet

metal ducting, insulating pipes and tanks,

and installing electronic control units. The

work will be nearly identical to the installation of sophisticated air-conditioning and

heating systems in conventional buildings.

Larger solar installations, such as those

serving groups of buildings and large industrial operations, are Iikely to require

supervisors, managers, draftsmen, designers,

and engineers in roughly the same proportion as these skills are required in the construction of conventional power-generating

facilities. In fact, since many large onsite

solar facilities are Iikely to be supplemental

to conventional boilers and generators, the

solar equipment would simply add work in

these areas at each installation, There may

be a shortage of engineers with adequate

knowledge in areas critical to onsite power

in general and solar devices in particular,

Designing a reliable and efficient onsite

device for a large installation (such as an

apartment or industry) requires experience

with other types of equipment not now conventionally used in utilities or buildin g

Employment opportunities in manufacturing are more difficult to define, since the

pattern of growth in the industry is presently

unpredictable. Work opportunities will include glazing, metal extrusion, component

assembly, and chemical processing (for photoelectric devices, selective surface formation, storage systems, etc.). It is difficult to

anticipate whether the employment will be

created in a large number of dispersed fabricating facilities, in large central plants, or in

both.

The skills required to maintain the type of

simple solar equipment installed on homes

and small apartments will be similar to

those required for conventional appliance

maintenance of utility gas and electri c

power equipment. Most of the personnel in

these professions will require additional

specialized training in solar technology.

There is a serious shortage of persons with

the skills needed to operate intermediatesized solar or conventional onsite energy

equipment. Owners of small total energy

systems report difficulty in finding an d

holding persons trained in operation and

maintenance of engines and heat recovery

units, energy control switching, and other

associated equipment. Maintenance of a sophisticated collector system will present

similar problems. Many now employed in

the operatio n of total energy system s

learned the requisite skills from the U.S.
Ch. VIl Impacts of So/ar Energy Ž 215

military services. Such training appears difficult to obtain in private industry.

Tables VI I-4 and VI I-5 demonstrate jobs

which must now be done to support conventional electric generating equipment. The

impact of solar equipment on jobs will depend on the extent to which solar devices

displace fuel consumption (replacing jobs in

mining with jobs in solar technologies), the

extent to which the technology would cut

the demand for peak generating capacity

(replacing jobs in constructing and maintaining generating equipment with jobs in solar

technologies), and the extent to which the

need for transmissio n and distribution

equipment wouId be reduced.

These effects are listed in the order of

their likelihood. It is most probable that

solar technology would initially affect only

fuel utilization, and would affect transmission and distribution requirements only in

an extreme case where all or much of local

energy needs are met with solar equipment

It should not be assumed that an increase in

solar utilization would necessarily replace

any of the employment indicated in tables

VI I-4 and VI I-5, The expected increase in

U.S. and worldwide coal demand is likely to

be so large that employment in minin g

would be unaffected by an expected penetration of solar energy into the market,

Several observations can be made on the

basis of the tables, however:

Ž SmalI solar installations are Iikely to

employ more blue collar workers than

Table VIl-4.—Skills Required for Constructing a Coal-Fired Electric Generating Plant

and Operating the System Over a 30-Year Period

1. Skills Required for Plant Construction (as a percentage of the 3,576 man-years required to

construct the plant and the transmission and distribution network) —

Coal-Fired Electric Transmission and

Generating Plant Distribution Facilities Total

Non-manual construction

work . .

Manual construction work .

Total construction work . . .,

9% 13% 22%

(63°/0 engineers and 25%

draftsmen and designers) 25% draftsmen and designers)

49% 29% 760/0

(variety of trades) (mostly electricians)
216 ● So/ar Technology to Today’s Energy Needs

Table VI I-5.— Detailed Breakdown of Skills Required for Conventional Electric System*

(man-years per 800 MWe coal-fired plant and associated distribution

and fuel facilities)

Annual

OperaI i

I 1110

31 186

1110

217

218 254

67 83

472

150

I I 33 I

,

523

6

6

3

1997

271

1148

240

3656

6

6

3

1474

60

1087

240

2861

240

450

1781

4

8

12

269

109

18

396

843

I 12

12

8

20

60

81

36

16

8032

10893

“ Based on Information In Manpower, Mater/a/s and Cap/ta/ Costs /or .Energy Re/a(ed Fac~/~fles, John K Hogle, et al , Bechtel Corp for Brookhaven National

Laboratory Associated Unlvers(l(es, Inc , Contract No 354617S, April 1976

professional employees. Solar installations on individual buildings typically

require one supervisor for each 1 0

workmen, 9 while the ratio for the conventional coal equipment shown i n

table VI I-4 is closer to 1 to 3, The larger

industrial and community solar systems

would, however, require much mor e

professional work.

Nearly 50 percent of the jobs

associated with operating and maintaining conventional equipment is associated with coal mining and transportaq FEA Project /ncjependence Task Force Labo r

Report
Ch. VIl Impacts of Solar Energy ● 217

●

tion. Jobs in these sectors could be

replaced with job s in repair and

maintenance of onsite equipment.

About 40 percent of the work required

to build a conventional electric system

and 30 percent of the work required to

maintain it is associated with distribution equipment, which is unlikely to be

affected by solar technology.

Working Conditions

Expansion of the solar energy industry

should not raise serious health or occupational hazards, but some of the possible

problems are discussed below. The manufacture of som e photovoltaic device s

employs cadmium and arsenic compounds

which couId present hazards to workers

assembling these units. Manufacture o f

plexiglass and other plastic s used i n

photovoltaic devices can also involve handling potentially harmful chemicals. These

manufacturing hazards are not unique, however, because these compounds are widely

used in other industries. Some steam-fitting

jobs will involve high-pressure steam lines,

and some proposed thermal storage methods will require very hot oiIs, possibly explosive or toxic. These issues deserve serious

attention before such instalIations become

common place. Devices using hazardous

material may only be employed in larger,

more centralized solar facilities and are

unlikely to be found in onsite residential

systems. Replacing jobs in coal mining for

those in solar equipment maintenance ,

however, would probably result in overall

improved working conditions.

Organized Labor

organized labor is enthusiastic abou t

solar energy’s potential for creating jobs.

Like many other construction trade unions,

the sheet metal workers (SMWIA) have been

hard hit by unemployment: the SMWIA has

a national unemployment rate of 30 percent

to 35 percent, with unemployment reaching

50 percent to 60 percent in some areas of

the North and Northeast ‘‘) These are regions

where energy prices have risen very rapidIy

in recent years. I t is possible that sizable

near-term markets for solar equipment can

be found in these areas in spite of their

re ativeIy unfavorabIe cIimates.

I n 1970, the plumbers and pipefitters had

a nationwide unemployment rate similar to

that of the sheet metal workers. A potential

labor problem associated with implementation of solar technology is the question of

which union will subsume the categories of

newly created jobs. Until recently there

have been few solar installations so that few

u n ions have staked out terri toritoriaI prerogatives. For the most part, the solar energy

field is still wide open to jurisdictional competition. The situation can be expected to

change as more work in the area becomes

available. An arrangement has already been

negotiated between the Sheet Meta l

Workers and the United Association o f

Plumbers and Pipefitters which calls for

joint crews in the installation of hot air collectors using liquid storage systems, Jurisdictional disputes could be a serious problem in other areas, however, unless al I issues

can be settled as amicably as this one has

apparently been.

Generally, union officials feel that an upsurge of solar construction and instalIation

would radically alter the number, not the

types of jobs available to union members.

Firms that now produce heating, ventilating,

and air-conditioning equipment— many of

them already active in solar collecto r

construction — would simply expand their

operations. Any new firms establishe d

would be unionized in conventional ways.

While labor has occasionally resisted the

introduction of new technologies into the

building industry, this resistance has always

been directed at technologies which reduc e

jobs on each building site or which transferred employment from one building trade

to another. The

‘” 1~ M( Monlgle,

1977

disputes associated with the

Siilhl’ I A, prlv,~te t ommu n I( ,~t Ion,

28-842 0 -15
218 ● So/ar Technology to Today’s Energy Needs

introduction of plastic plumbing, prehung

doors, and metal studs all resulted from one

of these effects. Solar equipment would add

work at each site without displacing work in

other areas, It is, therefore, difficult to imagine any group with a motive to resist its entry into the market.

LONG-TERM IMPACTS

The overall impact of generating a substantial fraction of U.S. energy from small

solar devices is hard to assess, since current

economic theory has no satisfactory method

for such analysis. None of the major price

equilibrium models used to determine the

future of U.S. energy supply and demand

adequately treat employment issues; most

make the overwhelmingly simple assumption that there will be full employment during the entire period analyzed. As a result,

many of these models tend to ignore the influence of alternative energy strategies on

unemployment, The difficulties of predicting economic impacts are magnified by the

lack of information necessary to translate a

workable theory or model into useful policy.

In the absence of an adequat e

methodology, the most critical questions involving the impact of solar technologies on

the work force cannot be answered with certainty. An example of one difficulty can be

seen in the problems associated with interpreting the implications of labor intensity. If

rapid rates of growth are expected in both

the U.S. economy in general and the energy

production sector in particular, and i f

unemployment is expected to be very low as

a result, any shift to a labor-intensiv e

technology like solar energy could prevent

wages from keeping pace with growth in

other sections of the economy, An industry

with high labor intensity requires more manpower for the same output than industries

with low labor intensity. As a result, the

average wage paid per worker must be lower

for the labor-intensive process. If growth is

not expected to be sufficient to eliminate

unemployment, labor-intensive industries

wiII be beneficial to both labor and society

by productively employing a larger fraction

of the work force.

Other questions which must be addressed

incIude:

1.

2,

3.

4.

5.

To what extent would the energy produced by solar equipment displace imports, nuclear, or indigenous fuel supplies? To what extent will solar energy

fulfill energy needs that might no t

otherwise be met? (If solar energy

fiIled such needs, employment could

grow i n areas of the economy not

otherwise possIble.)

To what extent will solar energ y

sources be able to reduce the need for

instalIing additional electric generating facilities as well as reduce the

demand for fuel?

If imports are reduced, and funds invested instead in U, S. solar industries,

how much direct and indirect employment would be created? How much

wouId employment be reduced in industries now benefiting from the export market stimulated by our purchase of foreign fuels?

What kinds of growth rates can be expected i n energy sources other than

solar energy? W i I I this growth rate

be constrained by a shortage o f

capital, resources, and demand, or by

a shortage of critical skills? Would

solar energy compete directly fo r

scarce resources or would it be able to

tap other capital or labor supplies?

What kind of work force dislocations

could be expected in a shift from one

energy source to another? Would new

skills not now available in the building

trades be demanded? What kinds of

transient unemployment could be expected?
Ch. VIl Impacts of Solar Energy ● 2 1 9

NET ENERGY USE OF SOLAR EQUIPMENT

Clearly solar energy devices cannot provide a useful contribution to the world’s

energy problems if more energy is used to

construct the devices than can be extracted

usefully from them. A brief examination of

this question indicates that solar equipment

can clearly be a net producer of energy. Unfortunately, no straightforward metho -

dology has been developed for computing

the total amount of energy consumed in

manufacturing, instalIing, and operating a

piece of mechanical equipment. Two different techniques will be used here: 1 ) computing the primary energy required t o

manufacture the materials used in the solar

collectors and conversion devices, and 2)

computing the energy used by assuming that

the energy used per unit investment in solar

equipment is the same as the nationa l

average energy use per unit of investment.

The results of both approaches are shown in

table VI I-6

PRIMARY ENERGY REQUIREMENTS

Energy requirements of silicon cells could

probably be reduced below the lowes t

number shown in the table if a technique is

developed for manufacturing thin cells from

amorphous silicon material. The amorphous

cells may require as little as 1 percent of the

silicon required in contemporary cells .

SiIicon celIs now require an energy consuming crystal growing process and the resuIting

crystals must be sliced into wafers. Both

processes waste a considerable amount of

s i I icon,

It should also be possible to reduce the

amount of energy required in the manufacture of many other of the products shown in

table VI I-8 if close attention is paid to

energy conservation. The energy content of

U.S. steel, for example, has declined by 25

percent since 1947, and the Germans use

about 68 percent as much energy as the

United States uses to manufacture stee].11

The Aluminu m Company of Americ a

(ALCOA) has apparently developed a smelting process capable of nearly halving the

energy used to manufacture alum inure. 2 It

can be seen from table VI 1-6, however, that

acceptable “energy-payback” times can be

achieved even if the materials are manufactured using 1970 U.S. technology.

It must be remembered that the energy

content of the solar devices shown does not

include any of the energy required in factories which assemble the collectors, the

trucks which deliver the materials to the factory and the collectors to the installation

site, the food consumed by installatio n

workers, or a number of other “secondary”

sources of consumption,

‘‘ M H Ross and R H Wllllams, Energy and

Economic Growth, printed by the )olnt E conom[c

Committee In Achlevlng the Goals of the Employment

Act of 1946— Thirteenth Anniversary Review, Volume

2, Energy Paper No 2, Aug 31,1971 (91-592), p 7

‘

2 J C Meyers, et al , Energy ConSUr-nptIOn in

Manufacturing, report prepared by the Conference

Board for the Energy Policy Project of the Ford Foundation, Ball lnger, Cambridge, Mass , 1974
220 ● Solar Technology to Today’s Energy Needs

Table VI I-6 .—Energy Payback Relations for Onsite Solar Conversion Systems

in Albuquerque

(See Tables VI I-7 & 8 for Assumptions)

Stirling Concentrating Flat plate Flat plate Pond thermal

engine in photovoltaic photovoltaic thermal colIector

tracking system array colIector

dish (100x)

1. energy required to

manufacture one square

meter of collecting

system (kWh/m 2

2. energy produced

by the s stem annually

2

(kWh/m/year)

—thermal . . . . . . . . . . .

—electrical + 

. . . .

(primary energy)

equivalent)

3. payback time computed from (1) and (2)

above (in months)

—payback from thermal energy . . . . . .

—payback from electric energy . . . . . . . . .

—payback from total

energy . . . . . . . .

4. allowed cost of system (in $/m2

) for a 1-

year energy payback

time assuming that

solar devices use the

same energy input per

dollar of initial cost as

the U.S. average of new

investments

—thermal . . . . . . . . . . .

—electrica l

450

1050

2069

425*-525 301 ● -8844 185-320 16-250

1440 —

1100 1000

5.1 4.4 (3.5)* —

2.6 5.7 (4.6)* 106 (3.6)*

1.7 2.5 (2.0)’

930

—

400-800

—

2.4-4.1 0.5-3.8

— —

2.4-4.1 0.5-3.8

88 120 77 33-66

172 291 83 (700$/kW) o —

—total . . . . . . . . . . . . . . 260 411 83 77 33-66

● Assumes advanced manufacturing techniques.

+ Average efficiency of electric generation and transmission distribution assumed to be 290/..

NOTES: It IS assumed that the engine used IS 32% efftclent and that the optical systems In the concentrators are 807. efflctent Flat.

plate slllcon cell arrays are assumed to be 120/. efflclent and concentrator cells are 20!/. efflclent (See volume 11, chapter IV

for detailed assumptions )

ENERGY USE PER DOLLAR OF GNP

One technique for counting all of the

energy which might enter a solar energy

system from secondary sources is to examine the average consumption of energy in

the United States per unit of GNP. 3 An examination of the incremental change in

energy consumption per incremental change

in GNP over the past 20 years shows that in

the United States about 12 kWh were consumed for each added dollar of GNP. The

average kWh consumed per dollar of GNP

has averaged 9-10 during the past few years.

(All quantities in 1976 dollars.) The link between GNP and energy consumption is the

‘ ‘ Technique suggested by Dr R D Huntoon, President, MEMO, Silver Spring, Md.
Ch. VIl Impacts of Solar Energy ● 2 2 1

Table Vll-7.– Materials Required in Solar Energy Devices (kg/m2)

Concentrator Concentrator Flat plate Flat plate Pond (thermal)

+ stirling + silicon s i I icon (thermal only) only

engine photovoltaic photovoltaic

Steel . . . 30 27 0-3 4-8 0

Glass . . . 16 16 6 6-12 0

Concret e 79 79 0 0 0-40

Sand . . . . . . 115 115 0 0 0

Polyurethane 0.3 0.3 0 0 0.6-6

Copper . . . . 0.4 0.4 0 4-8 0

Silicon cells . 0 0.0024 ’-0.007 0.24 ’-0.71 o 0

“Using advanced manufacturing techmques (not using amorphous slllcon)

Energy Content

SOURCES Concentrator data from H{ldebrandt, A F , and L. L Vant-Hull, ““Power with Heliostat s,”

Science 197 (1977). p 1139

SIIIcon data from L P Hunt ( Dow Cormng Corp I Total Energy Use in the Production of SI I Icon Solar Cells from Raw

Materials to F(n [shed Product The Conference Record of /he 72fh /EEE Photovo/ta/c S’pec/a//sfs Conference— 7976

Baton Rouge La Nuvember 1976 p 349

Other CO I Iector data from man ufaclurers

Table Vll-8.— Primary Energy Required to Produce Component Materials

for Solar and Conventional Power Systems

Total

energy

require- Source of input Energy (in percent)

ment Fuel

(kWh/kg) Coal Oil Gas Electrlcity byproducts

Polyvinyl chloride

resin, . 22 9.1 19.4 55,6 23,4 (7.5)

Portland cement

—wet proces s 2.1 30.4 13.7 39.9 16.0 —

—dry process. . . 1.9 42.6 8.0 32.4 17.0 —

Copper . . . . . . . 30 10.1 13.5 38.4 38.0 —

Steel ... ., 5.1 81.1 6.6 13.5 8.4 (9.6)

Glass containers . . 4.8 35.8 7.3 48.8 14.5 (6.4)

Silicon . . . . . 12400- – – – ~100 —

1050

SOURCES The Data Base The Potential for Energy Conversion In Nine Selected

Industries, FEA, June 1974, p 20

Silicon data from Hunt, L P

subject of consider-able contention 4 but it is

c I ear that the ratio is to some extent the

function of the society West Germany and

Sweden, for example, consume about twothirds as much energy per unit of GNP as

does the United States, although an exam i nation of recent Swedish data seems to

indicate that since the late 1960’s the incremental amount of energy consumption

per incremental amount of GNP in tha t

country has been close to that of the United

States. The statistics cited in the previous
222 Ž Solar Technology to Today’s Energy Needs

section at least indicate that it is possible to

shift energy consumption from the manufacture of primary materials to other areas

of the economy— areas where energy consumption per unit of value may not be as

great.

The allowable cost for solar energ y

systems capable of “paying back” th e

energy invested in them in one year (assuming the current U.S. ratio of incremental

energy to incremental GNP) is shown in

table VI i-6.

Since the allowed costs computed in this

may correspond to costs which can probably be achieved with solar devices, the

results of this method are roughly consistent

with the previous method; both indicating

that net energy should not present a barrier

to the use of solar energy. (It should be

noticed that if it is assumed that sola r

manufacturing is more energy intensive than

an average process in the economy by some

ratio R. then a solar system with a cost equal

to the allowed cost shown in the table would

require R years to pay back the energy it

contain s.)

THE IMPACT OF ONSITE ENERGY ON THE ENVIRONMENT

While solar energy equipment is not free

of adverse environmental effects, providing

energy from sunlight will have a muc h

smaller environmental impact than conventional sources providing equivalent amounts

of energy. The primary environmental effect

of utilizing onsite solar energy will be reduction of the potential adverse environmental

effects associated with other energy

sources.

The negative environmental effects of

solar energy devices stem primarily from

two sources: (1) land use requirements,

which could compete with other, more attractive uses of land, especially nea r

populated areas, and (2) emissions associated with the mining and manufacture of

the materials used to manufacture solar

equipment (manufactured steel, glass ,

alum inure, etc.). In general, solar devices

manufactured using conventional energy

sources, create more pollutants while they

are being manufactured than an equivalent

conventional plant (primarily because solar

equipment requires a greater capital investment per unit of output) but this assymetry

is outweighed by the fact that the solar

devices produce much less pollution during

their operational lifetimes. The net emissions associated with solar devices are much

smaller than those of conventional fuelburning plants.

Solar energy devices can change the

amount of energy absorbed by the Earth’s

surface, and could have some small effect

on the local thermal balance. The effect,

however, would typically be no greater than

the change in local climate produced by

covering land with equivalent areas o f

highways, buildings, or parking lots.

In addition to these primary effects, a

number of the specific storage and energy

tions of this study wouldl have advers e

environmental effects because of noise ,

local heat and other minor emissions, an d

use of toxic chemicals. These effects ar e

discussed in the chapers about individual

technologies.

DIRECT ENVIRONMENTAL EFFECTS

Emissions Associated With Operating

Energy Equipment

The primary direct impact of solar energy

on the local environment will be th e

elimination of adverse environmental effects attributable to the burning of conventional fossil fuels. The damage done to the

environment by conventional energ y

sources is well known, although the magnitude of the long-term health and climatic effects is still being determined. The large

number of ways in which producing electric
Ch. Vll Impacts of Solar Energy Ž 223

energy from a coal-f i red steam plant, for example, can adversely affect the environment are suggested below:

Strip mining required to harvest the

coal resources can permanently change

local topgraphy, alter stream beds,

disrupt or contaminate ground water,

and produce large amounts of rubble,

no i se, and dust in m i n i ng areas.

Reclamation can be difficult, par -

ticularly in areas where water shortages

exist. Underground mines have fewer

external effects, but can create safety

and health problems for miners

Processing the coal can produce large

amounts of solid waste and cause toxic

chemicals to be released into local

water.

Transporting coal can require the use

of trains which burn oiI or use electricity from some fossil source In some

cases new rail Iines will be required.

Burning coal produces large amounts

of airborne particuIates, sulphur and

niroge n compounds, hydrocarbons,

carbon monoxide, and a variety of

other a i r contaminant s In addition ,

large amounts of solid waste are produced either as coal ash or as by -

products of removing chemicals from

the smokestacks of the plants

Once generated, the electricity must be

transported along extensive networks

of transmission and distribution lines

Several recent studies have also indicated

that continued large-scale consumption of

fossil fuels could release so much carbon

dioxide into the atmosphere that the gas

wouId create aII green house” effect, raising

the average temperature of the Earth’s atmosphere by as much as 6 “C (11 “F) i n 100 to

200 years.15 The impact of such a climate

change on agricultural production and the

polar caps is difficult to predict. In addition,

the effect of using solar energy to replace

gas, oil, or wood home space and water

heating would be to reduce the thermal and

chemical pollution associated with these

means.

Negative environmental effects can also

be expected from other conventional approaches to electric generators. Electricity

provided from nuclear fission devices would

avoid many of the environmental impacts

associated with the consumption of coal,

but the nuclear process produces thermal

pollution and radioactive wastes with long

lifetimes. Hydroelectric facilities eliminate

most of the negative impacts of other electric sources, but can have a major impact on

land use because of the need to flood land

areas. Natural gas has fewer adverse environmental i m pacts, but reserves ar e

drastically depleted,

A comprehensive description of all environmental impacts of conventional energy

sources is beyond the scope of the present

study, but a brief comparison of the impact

on air and water quality by solar and conventional energy sources is shown on table

VlI-9). As a standard of comparison, table

VI I-9 also shows the energy needed by a

typical single family detached residence in

Omaha, Nebr., for 1 year (The exact characvolume 11, chapter IV. It can be seen that

use of natural gas is the environmentally

preferred approach of providing heat and

hot water to the house Even the solar total

A home which burns synthetic gas would

be responsible for considerably more air and

water poIlution than a home supplied with
224 . Solar Technology to Today's Energy Needs

Table Vll-9.—Ernissions Associated With the Energy Requirements of a Single Family House in Omaha, Nebr.

160-330 140-480

130-260 110-390

100-210 90-300

80-160 70240

60-120 50-180

50-100 40-150

9

7

5

4

3

3

(1 3-1 20)

13-120

(27-320)

(1 3-1 20)

50-440

50-510

40-400

35-320

27-250

20-190

20-160

NOTES — coal gass(flcatlon from unit fixed bed h[gh BTU plan! (see Synthellc Fuels Commerc(al(zatlon Program OP clt 1

net conversion eff(ctency of elecfrlc qenerat(on assumed to be O 29 and coal assumed to have 12000 BI u I b — coal plant uses f Iue gas scrubber

SOURCE The numbers on this chafl are based In parl on Information prov(ded by K R Smlfh John Weyanl and John Holdren Fvd/ud/IcIr? of

Corven/oo,) Powe/ Syslerns Un,v of Cal at Berkeley July 1975. p 119

processed to produce the synthetic gas.

Emission levels in this case, however, are

stiII below those associated with burning

coal directly for use in electric heating.

As the table shows, any of the coal-based

processes for producing residential energy

result in the release of large amounts of

emissions into the environment, For example, the house heated with baseboard heating units releases 160 to 330 Ibs. of nitrogen

oxides, 140 to 480 Ibs. of sulphur oxides, 9

Ibs. of hydrocarbons, 50 to 630 Ibs. of particulate, and nearly 2 tons of solid waste

per year. (These amounts include all direct

emissions associated with mining, processing, transporting, and burning coal at generating sites. ) The solar devices reduce these

releases in direct proportion to the amount

they reduce electricity consumption.
Ch. VIl Impacts of Solar Energy ● 2 2 5

The analysis has only considered environmental impacts resulting directly from

the burning of fossil fuels in mining, transport, or generating processes associated

with the production and transmission of

energy A number of processes indirectly

connected to the construction and operation of both conventional and solar equipment could also have adverse environmental effects — mining and refining materials

used to fabricate generating devices ,

transport equipment, and other energy production apparatus. All of these require

energy, and the production of the energy

resuIts in environmental damage. These

secondary impacts are extremely clifficuIt to

analyze quantitatively because an accurate

assessment would require a model broad

enough to encompass the entire economy. If

solar energy or other energy equipment increases the demand for steel, it is not clear

whether the indirect environ mental effects

can be computed simply by calculating the

energy required to construct this steel and

the damage charged to the account of the

energy source responsible, i.e., solar, since

the use of steel for energy equipment might

reduce the use of steel for other types of

equipment. Alternatively, the production of

additional energy could increase demand

for good s in the economy and in turn

stimulate energy consumption, thus increasing environmental damage by other sources.

Emissions Associated With the Manufacture

of Solar Energy Equipment

Since solar energy equipment typically

has a higher initial cost than conventional

systems, it is not surprising to find that

larger amounts of pollution are associated

with their manufacture (assuming that the

solar devices are constructed using energy

derived from conventional energy sources).

An estimate of the emissions associated

with the manufacture of various types of

solar energy devices capable of producing

the same annual energy output can be obtained by combining the information i n

tables VI I-7 and VI I-8 in the previous section

with the estimates of emissions associated

with different energy sources shown in table

VI I-10. Table VI I-11 presents the results of

this analysis by indicating the number of

months that several types of solar energy

systems would have to operate before the

emissions associated with providing a n

amount of energy equivalent to the energy

derived from the solar device equals the

amount of emissions associated with the

manufacture of the solar device. (The conventional system used for comparison is a

coal-fired electric generator. ) The resuIts are

roughly equivalent to the “energy-payback”

times computed previously.

The tables show once again the im -

portance of reducing the energy consumed

in manufacturing s i I icon photovoltaic

devices used without concentrators.

PROBLEMS ASSOCIATED WITH

ONSITE FOSSIL BACKUP

Solar energy systems which rely on onsite

combustion of fossil fuels as backup for

solar space heating and air-conditioning or

electric-generating equipment would have a

direct impact on air and water quality since

emissions would be released whenever the

backup systems were used. The total

amount of gaseous and solid polIutants produced by such onsite backup might be no

larger than the amounts produced by large

centralized generating plants providin g

equivalent backup services Emissions from

the onsite combustion would generally be

released much closer to popuIated areas

and, as a result, pollutants could have a

greater impact on health.

ONSITE SOLAR ENERGY SYSTEMS

AND LAND USE

The collectors employed in many of the

onsite solar energy devices discussed in this

paper can be either conveniently located on

the roofs of serviced buildings or gracefully

integrated into the surrounding landscape.

In a number of situations this will be impossible, and collector fields will require

and area which could probably be put to

other purposes. The resulting competition

for land will be particularly serious for on-
226 Ž Solar Technology to Today’s Energy Needs

Table Vll-10.—Primary Emissions Associated With Energy Resources Available for

Residential, Commercial, and Industrial Consumers

(pounds per thousand kWh of heating value reaching consumption site)

S02 NOX

1. Residential systems

—Natural gas . nil 0.3

—Oil (0.2%` sulphur) . . . . 0.75 0.3

—Electricity (from a ., 2.8- 3.3-

coal-fired baseload 9.6 6.6

generating plant) ●

—Synthetic gas ., . . . . 0.22- 0.75-

1.0 1.73

Il. Commercial and industrial

systems

—Natural gas nil 0.34

–Oil . . . . . . . . . . 0.75 1.71

—Coal (western-stoker) 3.07 1.88

—Coal (high sulphur) 4.1 0 1.71

Partic- Waste

CO HC ulates Solids Reference

—

0.7

0.10

0.14-

0.6

70.10

1.4

0.68

1,71

0,20

2,39

0.03 nil

0.06 0.10

0.11- 1,1-

0.19 10.2

0.063 - 0.49-

0.126 5,78

0.03 nil

0.68 0.34

0.06 16.0

0.06 0.20

nil (1)

nil (1)

431- (2)

533

106- (1)

199 (3),(4),

nil (1)

nil (1)

28.3 (1)

123.9 (1)

“Assumes a Ilme-scrub&r, flue-gas, desulfunzatlon system.

SOURCES: 1 Evaluation of the Feaslblllty for Widespread Introduction of Coal Into the Res{dentla[ and commercial

.% CtOrS, Voiume 1, prepared by the EXXON Research and Engineering company for the Center fOr

Environmental Qualltv Draft report, dated April 1977, p. 8

2- Evaluation of Conventional Power Systems, prepared by the Energy and Resources Program of

the Unwerslty of California at Berkeley. July 1975, P 1 1 9

3 Kirk R Smith, John Weyant and John f-foldren ” Evaluation of Conventional Power Systems, Unlverslty

of Call fornw at Berkeley, July 1975, P 136

4 Synthetic Fuels Commerclallzatlon Program Draft Environmental Statement, Synfuels Interagency

Task Force on Synthetic Fuels, Volume IV, December 1975, PP IV-12 and IV-40

Table VIl-11 .–” Payback Time” for the Emissions Associated With the Manufacture of

Solar Energy Systems

(expressed as the number of months the system must operate to

displace energy which, if generated in a coal-burning electric

generating facility equipped with a scrubber, would equal the

emissions associated with the manufacture of the solar device)*

Solar Energy System

Pond Flat-plate Flat-plate Concentramission Type

Concentrator with

(thermal (thermal (silicon ing photo- high efficiency heat

only) (only) photovoltaic) voltaic with engine.

siIicon cells

(electric only electric only thermal only

1. S0 2 . . . . . . . .03-1.4 0.6-1.1 3.3-106 6.1 2.9 1,1

2. NOX . . . . . . . . .05-1,8 0.6-1.3 3.4-106 6.0 2.8 1.1

3. co . . . . . . . . . . 0.5-15 3.7-7.5 5.1-109 26 14 5.1

4. Hydrocarbons. 0.3-8.0 2.0-4.1 3.9-109 15 7.6 2.9

5. Particulate. . . .08-4.4 1,7-3.4 3.7-108 24 13 5.0

6. Waste solids . . .02-0.6 0.3-0.6 3.2-106 2.5 0.9 0.3

‘These t(mes assume that emlsslons associated vwfh eleclrlc generation are the medan of the values given In table Vll 10
Ch. VII Impacts of So/ar Energy . 2 2 7

site solar systems where the required Iand is

close to populated areas. The land clearing

required for collector fields under these circumstances and the denial of alternative

uses of open land close to Iiving areas constitute by far the largest negative impacts of

this type of onsite solar technology. Conventional energy sources also require substantial land areas for mining, and for generating

and transmitting power, but much less land

is required per unit of energy produced and

the land, for the most part, is remote from

densely populated areas.

The land use issues cannot be dealt with

in general terms, The eventual outcome of

each case wilI depend on the skill and imagination of architects and planners as welI as

the tastes and values of the individuals and

communities served by solar equipment.

Negative impacts of collector fields on

land use will be evaluated in three

areas:

● building orientation and Iandscapi

● community design

Ž the environmental effects of colI

fields.

main

ng

ector

The following discussion will point out

some of the anticipated problems in this

field, and outline some possible techniques

for resolving difficuIties.

Land Use Impacts Associated With Building

Orientation and Landscaping

The environmental impacts of solar energy devices can be reduced in most cases by

placing as many collectors as possible on

the roofs or walls of buildings. (The impact

on building design and appearance and the

amount of area available for different types

of architecture will be discussed in the next

section. ) In many cases, however, it will be

impossible to find enough area on buiIdings

for an efficient solar syste m Existing

buildings may be shadowed during the day

or may have sloping roofs which are not

properly oriented for efficient solar collection A detailed study of the number o f

buiIdings In different regions having proper

solar orientations would be extremely valuable in assessing the potential market for

retrofitting existing structures with solar

equipment.

Orienting new buildings to maximize opportunities for collection of availabl e

sunlight can create problems. I n most new

communities the orientation and placement

of buildings is dictated by the location of

sewers, water Iines, electric mains, local

topography, main access roads, etc. The

direction of the Sun is rarely a consideration. Proper orientation of buildings for

solar energy purposes could increase the

cost of houses in the community; for example, services for providing utilities might

have to cover greater distances, driveways

might have to be extended to permit cars to

enter garages or carports which were not

facing the street, etc. These, and other

aspects of community design, wouId promote energy conservation which inevitably

will become more important to buyers as

the price of energy increases (see figure

VII-3).

In some situations a building constructed

to take maximum advantage of the Sun will

not supply enough roof or wall area for the

required collectors. The site itself may be

shadowed during the day, or basic requirements of the building may limit available

alternatives. I n a highrise buiIding, for example, the roof area will not be adequate for

more than a simple solar hot water system,

but more area can be obtained for solar collector if the south-facing wall is partially

covered by collectors (vertical collectors

gather 50 to 75 percent of the energy which

would have been provided by collectors

with the same surface area oriented at an

optimum angle on the roof).

Since the combination of roof and wall

areas may not adequately provide more

than a small fraction of the energy re -

quirements of some buildings, additional

colIectors must then be placed in arrays on

the ground It may be preferable to locate

these additional collectors close to th e

buildings served by the solar equipment,

since this wouId maximize alternatives for
228 ● Solar Technology to Today’s Energy Needs

Figure VII-3–A Small Housing Development Using Solar-Heating Devices

SOURCE Mother Earth News, No 45, May-June 1977, p IWO

multiple use of the collector areas and

minimize the cost of transporting the energy

produced by the collectors.

Many proposed multiple land uses would

coordinate collector fields with other land

uses. For example, solar collectors could

shade the upper level of parking lots (as

shown in figure VI 1-4), or in other cases the

colIectors couId shade patios or playgrounds. Lawn or shrubs can be grown under

the collectors as figure VI I-5 shows.

Wide spacing of collectors, or the placement of collectors on poles over parking

lots, will increase the price and possibly

reduce the efficiency of the collecto r

system. These effects must be carefully

weighed against the advantages of reducing

the system’s land-use impacts. There is room

for much creative work in this area which

wilI require a judicious mixture of engineering, landscaping, and building desig n

concepts.

Solar Collectors and Community Design

To design a new residential community or

commercial area for the maximum use of

solar energy is easier than to implement

solar collection in individual situation s

since, for example, plans can be made to

orient buildings properly, height restrictions

can be used to minimize shading, and areas

can be set aside for collector fields t o

reduce their disruptive effect on the community and maximize the likelihood o f

multiple land use. A variety of community

designs maximizing the use of solar energy

are possible, but problems are associated

with each.

If it is not physically possible or

economically desirable to locate collectors

close to building sites, the question o f

locating sufficient collector areas arises. It

must be determined, for example, whether

the system should be located in a remote

area, generating only electricity, or whether

the system should be located closer to the

community or industry served, and generating thermal energy as well. Remote location of the solar energy systems would permit the use of less expensive land, and

would avoid the problems associated with

competing for scarce open areas close to

population centers but it would increase

transmission costs and possibly reduc e

design fIexibility (see chapter IV).

Another possibility applicable especially

in new developments, would be to centralize the collector field and distribute the

community around it. Multiple land uses

would be encouraged by allowing centralized parking or some recreational areas to

be combined with collector fields but the

reduction in the density of the community

could result in added expense for other urban services (roads, utilities, etc.).
Ch. Vll Impacts of Solar Energy ● 2 2 9

Figure VII-4– Tracking Collectors Mounted Over a Parking Lot

The prohibitive expense or simpl e

unavailabiIity of land close to population

centers will be major constraints on the use

of onsite solar facilities in or near existing

communities. If solar collector fields are to

be integrated into population centers, factors such as population patterns, the size

and location of trees, the types of buildings

found in the area, etc., must be considered.

The use of solar energy in individual

buildings can be encouraged by intelligent

community planning , In the computer -

modeled residential community of 30,000

400,000 to 600,000 square meters of a area

highways. If all of these areas were covered

with s i I icon photovoltaic devices and if adequate storage were available a continuous

output of 17 to 28 MW i n Omaha, Nebr, and

23 to 37 MW in Albuquerque, N Mex , could

be provided. While this wouId not be adequate for all of the community’s needs, it

wouId greatIy reduce the land requirred for

ground-mounted colIector arrays.

It may be very difficult to design a solar

community in a heavily forested area and

trees in existing neighborhoods may present

prohibitive problems for some sites. A great
230 Ž So/ar Technology to Today’s Energy Needs

Figure VII-5.—Vegetation Growing Under Arrays of Solar Collectors

Photo by John Furbet

a) Professor Francia’s Solar Steam Generating Plant, Genoa, Italy.

b) Flat-Plate Collectors at University della Calabria, Cosenza, Italy.

SOURCE G Franc!a, Unlverslty of Genoa, Italy
Ch. VII Impacts of Solar Energy . 231

deal of thought will have to be given to this

issue i n some parts of the country and there

may be no easy solution

THE ADVERSE ENVIRONMENTAL

EFFECTS OF COLLECTOR FIELDS

If land must be cleared exclusively for use

as coIIector fields, the effect o n the IocaI environment could be very great I m pacts include the loss of existing buiIdings, the

destruction of ecosystems, and the noise,

dust, and disruption of the clearing activity.

If the land were originally forested, the fundamental ecology of the region would be affected While it is possible for vegetation to

grow under collector fields, so that some

low plants and smalI animals could continue

to Inhabit the area, the mixture of species

would no doubt be very different from those

which wouId have inhabited the region had

it remained undisturbed Moreover the access roads required to maintain the collectors would disturb any new species which

did inhabit the area. If the land wer e

originally grassland or desert, however, the

impact of the solar devices might be less,

although it in no way could be considered

negligible. Some change could be expected

in local temperatures simply because the absorptivity of the region would be changed

by the presence of the collectors. The effects caused by solar arrays, however, are no

different from the changes which would occur from other types of development (e. g.,

with a parking lot or with a farm field). Any

harm to a relatively undisturbed natural environment in the immediate vicinity of

populated areas must be considered to be

particularly serious, because such areas are

rapidly disappearing.

LAND USED BY CONVENTIONAL

GENERATING SYSTEMS

A conventional coal-fired electrical generating system requires land for mining, train

lines to transport the coal, land for the generating facility, and land for transmission

and distribution of power.

Table VI 1-12 indicates the amount of land

which would be required for strip-mining

coal and for transmitting power. Each

square meter of strip-mined land in the

Eastern United States yields enough coal to

provide about 2,000 kWh of electric energy.

A silicon photovoltaic array placed over the

same square meter would need to operat e

Table VII-12. —Land Required for Strip-Mining Coal

Eastern strip mines Western strip mines

1974 1985 1974 1985

Acres/year mined . . . . 57,348 69,704 7,140 16,330

kWh/m 2 . . . . . . . . . . . . 2,150 2,144 5,744 10,627

Years of solar operation to provide equivalent power in the

same land area:

Albuquerque . . . . . . . . . 14 14 38 69

Omaha. . . . . . . . . . 22 22 60 111

Assumptions: —

—

—

—

29 percent efficiency of generating and transmitting

electrlcity

Silicon photovoltaic cells on non-tracking racks

spaced to avoid shading (land coverage ratio = 52

percent in Albuquerque and 43 percent in Omaha),

12,000 Btu / lb coal

Coal production statistics based on OTA forecasts.
232 Ž So/ar Technology to Today’s Energy Needs

between 14 and 22 years to provide an

equivalent amount of energy. In the West,

where thicker coal seams are found, a

square meter of strip mine could provide

between 6,000 and 10,000 kWh of power and

a colIector would need to operate 40 to 100

years in the same region to provide an

equivalent amount of power.

Long distance electric transmission also

requires a considerable amount of land. The

Electric Power Research Institute estimates,

for example, that by 1990 electric transmission Iines will require a right-of-way of 2. I x

10 10 m

2 (about 220 billion ft2

). ” If this area

were covered with 10-percent efficient solar

cells, about 4 x 1012 kWh (1 3.6 Quads) of

electricity would be produced annually, It is

possible to use the rights-of-way of transmission Iines for purposes other than transmission — multiple land use is also possible with

the solar equipment but somewhat more diff i cult and expensive to undertake.

Another interesting point of reference for

the land use impact of solar equipment is

the land covered by surfaced roads in the

United States. There were about 5.9 x 1 0

1 0

m

2 of such roads in the United States in

1975.17 Covering these surfaces with 10-

percent efficient cells would produce 11.4 x

1 0

12 kWh annually or 39 Quads. Unite d

States electricity consumption in 1976 was 2

x 10’ 2 kWh or 6.8 Quads.

The direct comparisons of solar and conventional land use cannot be conclusive,

These comparisons do not account fo r

either the quality of the land impacted by

the two types of systems or the fact that the

impacts of onsite solar facilities are typically closer to populated areas than coal

mines or larger transmission facilities. Landuse impacts in populated areas are generalIy

more regulated by local zoning laws and by

the public opinion associated with highly

visible local activities, whiIe activities in

remote areas are generally exempt from

reguIation.

IMPACT ON BUILDING DESIGNS

BACKGROUND

Unlike conventional heating and cooling

equipment, solar colIectors mounted outside of the building can be highly visible.

Concern about the appearance of solar instalIations and the effect of this appearance

on the resale value of the property to which

it is attached, may be a significant barrier to

the near-term commercialization of onsite

solar energy equipment. In a recent survey

of lending institutions, 43 percent of the officials interviewed stated that concer n

about the “bulkiness or unusual appearance” of solar devices would be of some

“ EPRI Technical Assessment Guide, August 1977.

‘

 7 Federal Highway Administration, Department of

Highways, 1974. (Calculation assumes average surfaced road width is 40 feet )

concern to them in evaluating a loan application for solar energy and 19 percent stated

that this would be a “primary concern.’” 8

The difficulty is traceable in part to the

lack of examples of equipment on standard

types of housing and to the fact that most

publicized devices are either highly experimental (without great attention being paid

to appearance) or are installed on expensive,

custom-built homes. With some care, even

buildings which are optimized for sola r

energy by having large roof areas with steep

slopes, large south-facing windows, thick

walls, and other special features, can be

made attractive.

18 Regional and Urban Planning Implementation

Inc , financing the So/ar Home: Understanding and /rnproving Mortgage Market Receptivity to Energy Conservation and Housing Innovation, June 1976, p. 83
Ch. VII Impacts of So/ar Energy ● 233

integrating active and passive sola r

energy systems into building design will require some imaginative architecture and the

results will depend on regional tastes. It is

possible to design conventional buildings

with solar energy devices with a minimal impact on building appearance (see figures

VI I-6 and VI 1-7). Collector colors can be

matched to root colors.

The feasibility of retrofitting existing

homes with collector s

figures will depend o n

Shading by improperly

other buildings present

as shown in th e

local conditions.

placed trees and

the most serious

problems, and improper roof orientation or

slopes could impair system efficiencies.

The roofs of standard buildings are not

designed to optimize the efficiency of solar

equipment. Roof pitches may be wrong, the

roof area may be too small, the framing of

the roof may be insufficient to support a

collector, and the orientation of the structure may be incorrect. Table V I 1-13 indicates

the roof areas available in standard building

designs, and the areas which can be provided with roof slopes at more optimum angles

for solar collection. A number of imag -

inative designs have been developed during

Figure VII-6– Techniques for Integrating Solar Collectors

Into Conventional Designs for Single Family Residences

SOURCE Solar Dwelling Design Concepts op clt pp 79.83, 89

28-84’2 () - 16
234 ● Solar Technology to Today’s Energy Needs

Figure VII-7– Techniques for Integrating Solar Collectors Into

Conventional Designs for Townhouses and Low Rise Apartments

the past

SOURCE Solar Dwelling Design Concepts op clt pp 91-93

few years which can provide larg e

collector areas at proper orientations. Two

such designs are illustrated in figures VI I-8

and VI I-9.

The less attractive collector systems, such

as tracking colIectors and rack-mounted flat

plate collectors, can be shielded fro m

ground view with simple screens around the

building perimeter, but in some installations

it wilI be clifficult to mask the systems completely. (See figure VI I-10). Screens would

add to the cost, but would probably increase the reliability of tracking systems by

also serving as wind screens. As society has

apparently become accustomed to buildings with all manner of gadgetry on roof

tops (vents, antennas, and air-conditioning

cooling towers), it would be difficult to

argue that the addition of solar devices

would seriously degrade the appearance of

buildings.

Wall collectors provide another means of

increasing the collector area. Large, tal l

buildings, such as high-rise apartment buildings, are particularly well suited to wall collectors. Wall collectors generate about 7 5

percent of the energy that the same collector area wouId generate if tilted (in Omaha ,

Nebr. ), so their use may be economical in

may not aIter the appearance of some types

of buiIdings, e.g. , glass-waIled offices, o r

apartments (see figure V I 1-11 )
Ch. VIl Impacts of Solar Energy ● 235

Table VII-13 .—Potential Areas for Collectors on Typical Buildings*

(in square meters)

Albuquerque Boston Ft. Worth Omaha

Shopping Center

Building Roof

Horizontal roof area .

Slanted racks on horizontal roof . . . .

Parking Lot

Land area, . . . . . . .

Slanted racks above

cars . , . .

196-Unit high rise

Building Roof

Horizontal roof area . .

Slanted racks on horizontal roof . . .

500/0 of southern wall.

Parking Lot

Land area. . . . . . . . . . .

Slanted racks above

cars . . . . . . .

36-U nit low rise

Building Roof

Horizontal roof area .

Slanted racks on horizontal roof . . . .

Parking Lot

Land area. . . . . . . . .

Slanted racks above

cars . .

8-Unit townhouse

Building Roof

Horizontal roof area .,

Roof slope at latitude

Typical roof slope

Slanted racks on horizontal roo f

Parking Lot

Land area, . . . . . . .,

Slanted racks above

car s

Single family house

Building Roof

Horizontal roof area

Roof slope at latitude

Typical roof slope .

Slanted racks on horizontal root. . . . . .

Carport

Horizontal roof area .,

Roof slope at latitude

Slanted racks on horizontal roof . .

28,800

15,261

90,000

47,691

1,883

998

1,500

7,840

4,154

1,270

674

1,440

763

620

756

327

328

320

170

83

101

44

44

28

34

15

28,800

12,171

90,000

38,034

1,883

796

1,500

7,840

3,313

1,270

537

1,440

609

620

837

327

262

320

135

83

112

44

35

28

38

12

28,800

16,520

90,000

51,624

1,883

1,080

1,500

7,840

4,497

1,270

729

1,440

826

620

731

327

356

320

184

83

98

44

48

28

33

16

28,800

12,626

90,000

39,456

1,883

826

1,500

7,840

3,437

1,270

557

1,440

631

620

824

327

620

320

140

83

111

44

36

28

37

12

“See volume 11, chapter IV for a detatled description of the bulldlngs
236 ● So/ar Technology to Today’s Energy Needs

Figure VI I-8.—A Residential Building With Optimized Solar Roof Pitch and Orientation

ROOF PITCH AND ORIENTATION

Table VI 1-14 indicates how the energy collected by flat-plate collectors varies as a

function of the angle of the roof and orientation of the building. It indicates the “useful” output of thermal collectors (e.g., the

output which is actually applied to heating

space and water), the total thermal output

(which includes thermal energy which must

be discarded because the storage is filled),

and the electric output which could be provided by a flat-plate silicon photovoltaic a rray. In all three cases, the direct output is

shown and the results are normalized for

comparison with the optimum roof design.

PHOTO: Reprinted from Popu/ar Science with permission 1976 Times Mirror Magazines, Inc

The useful thermal output for heating and

hot water is optimized when the roof in

Omaha is sloped at an angle of 560 (which is

150 greater than the latitude), and the colIector is oriented due south. If the collector

faces south but is tilted at an angle more

typical of residential roofs (a drop of 4 feet

in a run of 12 feet) the performance would

be reduced by 18 percent or, equivalently,

the amount of collector area required for an

equivalent output would need to be in -

creased by 22 percent. If the house with a

collector tilted at the latitude angle (4 I 0,

were oriented due west instead of south, the

energy received would be reduced by 11 percent. If both effects were combined in a
Ch. VIl Impacts of So/ar Energy Ž 237

Figure VII-9. —A Commercial Building Designed To Optimize Roof Pitch and Orientation

‘‘worst possible house for solar cilIection, ”

and a house with a standard “4/12“ slope

were facing due west, the energy received

per unit collector area would be reduced 3 9

percent or the required collector area would

be Increased by 64 percent. [Even a house

with a collector on a horizontal roof would

receive more energy. ) A number of other

combinations of roof pitches and building

orientations are shown for comparison.

The output of photovoltaic devices i s

much less sensltive to the roof orientation, A

south-facing roof tilted at the “4/12“ slope

wouId receive 98 percent of the energy received by a house tiIted at an optimum

PHOTO Courtesy of J Bayless, President, Solaron Corporation, 1976

This analysis indicates that a large fraction of existing buildings could be retrofitted with solar systems without either a

major sacrifice in system efficiency o r

alterations in the roof lines. It also means

that architects have considerable latitude in

designing solar structures; deviating from

optimum orientations will increase the cost

of collector systems, but designers may feel

that this added cost is justified if it allows a

more attractive buiIding plan, if it improves

the orientation of the building with respect

to scenery, or if it reduces the overall construction cost of the buiIding.

SPACE FOR STORAGE

Storage Tanks

The size of required heat storage tanks

varies with the type of storage sought: over-
238 ● So/ar Technology to Today’s Energy Needs

tor 

night storage, backup capacity for 2 or 3

days to allow for cloudy weather, or seasonal storage. For overnight heating and hot

water needs (assuming an average house in

Omaha on a typical winter day), a 500 to

1,000 gallon water tank is sufficient, For 2 to

3 days storage, that capacity would have to

be doubled or tripled; seasonal storage

would require a 50,000 gal Ion tank,

For the 196-unit apartment building (again

using the needs on a typical winter day in

Omaha), overnight storage would require a

25,000 to 50,000 gallon tank; 2 or 3 day

storage capacity would be twice or three

times that, and seasonal storage would require a 3 to 6 m i I I ion gaIIon tank

All but the smallest of these tanks would

probably be buried close to building sites,

thus minimizing land and building space requirements. In the case of new housing, it

might be more practical to bury the tank

directly under the basement of the house,

creating a sort of sub-basement. On most

sites, there should be adequate space for
Ch. VII Impacts of Solar Energy Ž 239

Figure VI I-1 1 .—Use of Collectors on the

Vertical Wall of a High Rise Hotel

I

I

I

SOURCE The Radlsson Hotel Comoratlon St Paul Mlnn expected operational date September 1978

even the largest tanks The huge tanks required for seasonaI storage i n apartments,

for example, could be buried in an area

covering less than half the area of the apartment’s parking lot.

A number of storage media other than

water are avaiIable: oiIs, salt cornpounds,

organics, and concentrated solutions. The

alternate fluids have the advantage of requiring less volume and hence less storage

spac e< but the disadvantage of greater expense, flammability, or the requirement of

separate speciaIly constructed tanks must

be considered Since the tank is buried, its

size IS not an aesthetic factor, and water

tanks are probably the most practical for the

residential and commercial applications dis -

cussed here.

Electrical Storage Devices

Advanced collector systems may produce

electrical energy for a residential or commercial buiIding as welI as thermal energy,

and onsite storage of electrical energy in

batteries may be a necessary component of

such systems.

The space required by the batteries is, by

itself, not a major concern. Lead-acid batteries require about 1 cubic foot of space

cubic feet of space, most Iikely in the basement of the home (less than a 3-toot cube). A

bank of batteries with this capacity would

be dangerous, particularly in residential

uses where children are present, and should

be stored in a locked room or cage of some
240 Ž“ Solar Technology to Today’s Energy Needs

Table VI.14.—Thermal and Electric Outputs of Flat-Plate Collectors in Omaha,

Nebr., as a Function of Tilt Angles (with respect to horizontal)

and Orientation (with respect to south)

Orientation

South

Tilt = Lat + 15° 590 .91 410 1.00

South

Tilt = Lat 643 .99 399 .97 226 .99

South

Tilt = Lat -10° 647 1.00 378 .92 228 1.00

South

Tilt = Lat -23°

(4/12 roof slope) 613 .95 335 .82 224 .98

Tilt = Lat 598 .92 364 .89 216 .95

Tilt = Lat -23°

(4/12 roof slope) 470 .73 249 .61 195 .86

Horizontal 502 .78 260 .63 205 .90

S. Vertical 326 .50 324 .79 127 .56

W. Vertical 169 .26 158 .39 112 .49

14.6

13.6

11.9

13.2

8.1

8.7

6.3

5.0

21.3

22.6

23.7

21.3

23.1

24.0

13.8

13.0

Assumptions: —

—

—

—

thermal output computed assuming a tubular flat plate (operating

characteristics of the collector assumed in the analysis are

shown in volume II chapter IV).

useful output of the collector was computed assuming that a

heating and hot water system with 40 m

2 of collectors is used in

connection with 1,000 gal of hot water storage and serves the

typical single family house whose characteristics are outlined in

volume II, chapter IV. Electric resistance heating and electric

hot water heaters were assumed to provide needed backup.

the photovoltaic system analyzed was a passively cooled silicon

system with a cell efficiency of 0.14 at 28° C and a heat removal

factor (Ke

) of 0,025 kW/m2 -“C.

the results are integrated over a full year.

SOURCE: Prepared by OTA.
Ch. Vll Impacts of So/ar Energy ● 241

sort. The 196-unit apartment building would

need a I most 3,000 kWh of electrical storage

for one day’s needs (about a 15-foot cube).

In addititon to the security needed for a

large array of high-yield batteries, the system should be vented to protect against the

buildup of potentially explosive hydrogen

and the toxicity of other gases which are byproducts of lead-acid battery use (see chapOTHER BUILDING IMPACTS

Onsite energy systems will undoubtedly

require more interior building space than

conventional heating and cooling systems.

Even the simplest hot water systems require

space for pumps, controls, and larger hot

water tanks. More complex heating systems

will require larger tanks as well as additional

pumps, controlled valves, and heat exchangers. While the tanks can

the building, space will

supporting equipment.

space needs wiII be minimal.

b e

be

In

buried outsid e

required for the

most cases the

More complex systems using heat engines

would require substantially more space,

either in the building or in sheds close to the

building served, A solar heat engine large

enough to operate an air-conditioning system, for example, would be approximately

as large as the air-conditioner which it

operates An engine providing electricity as

welI as air-conditioning wouId be eve n

larger. Space requirements within buildings

could present serious difficulties in these

cases.
Chapter Vlll

COLLECTORS

Chapter VIII.–COLLECTORS

Page

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245

Major Design Considerations , . ..........246

Tracking Versus Nontracking Systems. .. ..246

Installation. . . . . . . . . . . . . . . . . . . . . . ......248

Working Fluid.. . .......................249

Survival in Adverse Conditions . ..........249

Surveyof Collector Designs. . ..............250

“Passive’’ Systems . ....................250

Siting . . . . . . . . . . .....................250

Basic Architectural Considerations .. ...251

Stationary Flat-Plate Collectors. . .........255

Pond Collectors. . :. . . . . . . . . . . . . .. ....257

Flat-PlateCollectorsAssembled Onsite. .259

Factory-Assembled Modular Collectors. .259

Tubular Solar Collectors. . ...............261

Concentrating Collectors. . ..............261

Nontracking Concentrating Systems ....26l

ActiveTracking and Concentrating

Systems . . . . . . . ...................264

Environmental Impacts. . ..................284

Working Fluids. . .......................284

Manufacturing Hazards . ................284

Collector Costs . . . . . . . . . . . . . . . . . . . . . . . . . .285

FOB Collector Prices . ..................285

Collector Summary Tables. . .............285

Collector Performance . ...................287

The Energy Available for Collection . ......289

The Solar Resource. . . . . ..............291

CollectorTracking Geometry. . ...........295

Collector Losses . ......................295

Optical Losses.. . ....................295

Thermal Losses... . ..................298

The Significance of the Loss Factors . . . . 298

The Net Performance of Collectors. . ......300

AppendixVlll=A.-Techniques Used to

Compute the Output of Representative

Collector Designs . ...................303

LIST OF TABLES

Table No, Page

Degradation in the Performance of FlatPlate PhotovoltaicArrays Located in Cleveland, Ohio, September-December 1975....248

SiteOrientation Chart. . ................251

Characteristics of Competing Designs for

the 10MWeSolarCentral Receiver

Powerplant. . . . . .....................280

Stationary Flat-PlateCollectors. . ........286

Foreign StationaryCollectors on U.S.

Market . . . . . . . . . . .....................286

StationaryTubularand CPC Collectors ...287

One-AxisTracking Collectors . ..........288

Two-AxisTracking Collectors . ..........289

Assumed Coilectorlnstallation Costs for

VariousCollectorConfigurations,

ExcludingOverheadand Profit . .........290

Useful Radiation lncidenton Flat-Plateand

FullyTracking Concentrating Collectors,

FourCities, in kWh/m2/year . ............298

CollectorCharacteristicsAssumed in

Preparing FigureVlll-39 . ...............299

Comparison of the AnnualOutput of Five

CollectorDesigns, in kWh/m2/year. .. ....301

Output of SingleCoverand DoubleCover

Pond Coilectors for Various Operating

Conditions . . . . . . . ....................301

A-1. Empirically Derived Constants Used in the

FormulaforEstimating Direct Normal

Radiation,Given Measurements of Total

Horizontal Radiation.. . ................304

A-2. Comparison of 1962 Weather With LongTerm Averages and Extremes . ..........304

A-3. Glossary of Symbols Used in Computing

Collector Geometry, . ..................306

A-4. Coefficients of the Fourier Expansion

of the Equation of Time Used in Equation

A-15. . . . . . . . . . . . .....................309
Chapter VIII.—COLLECTORS—continued

LIST OF TABLES—continued

Table No. Page

A-5. Transmittance of Transparent Covering

Materials Which May be Used in Solar

Collectors. . . . . . . . . . . . . . . . . . . . . . . .. ...311

A-6. Specular Reflectivities . ...............313

A-7. Maximum Possible Geometric

Concentration Ratios at Perihelion. . .. ...320

A-8. Maximum Possible Geometric

Concentration Ratios . .................320

A-9. Typical Thermal Loss Coefficients .. ....322

A-10. Ratio of Collector Output When Average

U-Value Used to Output of Collector With

Variable U-Value for Flat-Plate Collectors

in Omaha With Tilt Angle—Latitude. .. ...323

LIST OF FIGURES

Figure No. Page

1. A Sample Site Plan Illustrating Techniques

for Minimizing Heating and Cooling

Requirements . . . . . . . . . . . . . . . . . . . . .. ..252

2. The Operation of the Trombe-Wall

Collector/Storage System . .............254

3. A House Using a Trombe-Wall Collector

Located in Eastern Maryland . . . . . . . . . . . . 254

4. The Temperature Averaging Effects of

Masonry Wails of Various Thickness .. ...255

5. Typical Home With Solar Water Heating

Using Flat-Plate Collectors . ............256

6. Cross-Section of a Typical Modular FlatPlate Solar Collector. . .................257

7a. Pond Collector With a Rigid Cover .. ....257

7b. Cross-Section of a Combined Pond

Coilector/Thermal Storage Pond Using

an inflated Cover. . . . . . . . . . . . . . . . . . . . . .258

8. Typical Air Collector Installation . . . . . .. ..260

9. Various Tubular Collector Designs. .. ....262

10. Fiat-Plate Collectors With Stationary

Boosters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .263

11. One-Axis Compound Parabolic Collector. .264

12. Albuquerque-Western Tracking Collectors

installed on Modular Home . ............265

13. Acurex Parabolic Trough . ..............266

14. Beam Engineering Parabolic Trough on a

Polar Mount . . . . . . . . . . . . . . . . . . . . . . . . . . 267

15. (a) The Linear Fresnel Lens and the

Absorber Tube are Both Visible in This

Cross-Sectional End-View of the Northrup

Concentrating Collector. (b) Array of

Northrup Collectors is Mounted for Polar

Tracking . . . . . . . . . . . . . . . . . . . . . ........268

16. Receiver Pipe inside McDonnell Dougias

Prototype Linear Fresnel Lens

Concentrator. . . . . . . . . . . . . . . . . . . . . . .. .268

17. General Atomic Distributed Cllector

Concept . . . . . . . . . . . . . . . . . . . . . . . . . .. ..269

Figure No. Page

18. Russell Collector by Scientific-Atlanta,

inc., Installed at Georgia institute of

Technology . . . . . . . . . . . . . . . . . . . . .. ....269

19. ITEK Distributed Collector Concept With

20

21

22<

23,

Inset Showing the High-Performance

Receiver Design. . . . . . . . . . . . . . . . . . . . . .. 270

The Varian Two-Axis Concentrator Using

GaAs Photovoltaic Devices . ............272

An MIT Design for a Small Two-Axis

Tracking Unit . . . . . . . . . . . . . . . . . . . . .. ...273

Sales Price of Cast-Acrylic Fresnel Lens

Versus Production Volume . ............274

1 kWe Focusing Photovoltaic Test

Bed & Sandia Laboratories, Albuquerque.

l-Square Foot Fresnel Lenses Focus on

2-inch Diameter Solar Cells . ............275

24. RCA’s 300We Photovoltaic Concentrator. .276

25. JPL Paraboloid Design With Stirling Engine

at Collector Focus. . . ..................276

26. Sunpower Systems Solar Powerplant. .. ..277

27. Francia 100 kWt Solar Powerplant. . ......278

28. Mitsubishi (7 kW+) Heliostat/

29,

30.

32.

33.

34.

35.

36.

37.

38.

39.

Receiver Test Bed . . . . . . . . . . . . . . . . . . . . .279

Pilot Plant Heliostat Concepts. . .........281

Pilot Plant Receiver Concepts. . .........282

McDonnell Douglas 10-MW Pilot Plant

Design. . . . . . . . . . . . . . . . . . . . . . .........282

The 5-MW Central Receiver Demonstration

Under Construction in Albuquerque,

N. Mex.. . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..283

Cross-Section of Stationary Hemisphere

Concentrator . . . . . . . . . . . . . . . . . . . . .. ...283

Variation of Direct Normal Component of

Solar Radiation With Time . .............292

Mean Daily Total-Horizontal Solar Radiation

(kWh/m2) . . . . . . . . . . . . . . . . . . . . . . . . . ... .293

Mean Daily Direct-Normal Solar Radiation

(kWh/m2). . . . . . . . . . . . . . . . . . . . . ., .. ....294

Perfect Fiat-Plate Collector Tilted at

Latitude Angle and a Perfect Fully Tracking

Collector. . . . . . . . . . . . . . . . . . . . . . . . . . .. .296

Comparison of the Maximum Energy

Collectable by Four Types of Collectors

Located in Albuquerque (1962 Radiation

Data) . . . . . . . . . . . . . . . . . . . . . . ..........297

Energy Balance for Five Collector Designs 299

A-1. Collector Coordinates Showing the -

Collector Direction . . . . . . . . . . . . . . . . . . . . 305

A-2. The Geocentric and Collector Coordinates

Showing Direction of Sun. . . . . . .........306

A-3. The Specular Reflectance at 500 nm as a

Function of the Collection Angular Aperture

for Several Reflector Materials . .........312

A-4. Monthly/Hourly Variation in Available

Thermal Power...;. . ..................315

A-5. The Solar image on Three Typical

Concentrating Collectors. . . ............317

A-6. Characteristics of the image of Acrylic

Fresnel Lenses Designed by Swedlow Inc.

for Solar Applications. . ................318

A-7. Geometry of a Simple Flat-Plate

Collector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
Chapter Vlll

Collectors

BACKGROUND

This chapter reviews the diverse assortment of techniques which can be

used to collect sunlight on receiving surfaces. Technologies for converting

the energy collected into mechanical or electrical energy are examined in

chapters IX and X.

Solar collectors are the only components of solar energy systems which

are unique; all other parts of the systems—heat engines, storage devices,

and the like—have a history of use in other applications. Collectors can,

however, be relatively simple devices and have much in common with other

types of heat exchangers. A variety of design approaches are possible using

well-established technology. The major problem is reducing the cost of the

devices with innovative designs or mass production techniques. Low-cost

colIectors are critically important to the future of solar energy since collector

costs dominate the cost of solar energy in almost all systems.

Evaluating collectors at this stage in the history of the technology is an

extremely treacherous undertaking. The field is changing at a bewildering

rate and it is much too early to be dogmatic about the outcome. Since collector designs can be perfected without the need for sophisticated development

laboratories, a large number of inventors have entered the field and an incredible variety of approaches have been proposed. Concepts have come from

home inventors, university laboratories, and small manufacturing concerns,

as well as large Government and corporate development laboratories. Many

of these new ideas wilI never reach the marketplace and many that do will not

survive the intense competition which is beginning to take place. There are

presently about 200 independent organizations in the United States with a

collector on the market.

Many interesting designs have never been produced commercially and

many of the designs which have reached the market have been available for

such a short time that their long-term performance cannot be accurately

evaluated. In particular, few systems have been tested extensively in adverse

weather conditions. Moreover, many contemporary collector manufacturers

are smalI firms which are unable to make reliable estimates of a selling price

which can sustain the overhead and marketing costs of their concerns—

several companies have failed in the past year. As a result, the claims made

by many manufacturers of inexpensive devices must at this point be treated

with great caution.

Uncertainty about the reliability and performance of collectors may be alleviated to

a considerable extent when consensus

standards are developed by the industry for

testing collectors and when testing laboratories are certified for conducting the

needed tests. (This uncertainty about system

quality is a major problem for consumers

and is discussed more extensively in chapter

I I 1, Policy Analysis.]

I n almost all cases, forecasts of the future

price of collectors are based on estimates

of potential mass production and are not

based on a detailed analysis of specific

manufacturing processes, I n fact, the price

of many of the products now on the market 

is unlikely to fall dramatically with mass

production–the cost of materials already

represents a significant fraction of the total

cost of some devices. Significant price re245
246 ● Solar Technology to Today’s Energy Needs

ductions are more likely to result from the

development of innovative designs.

I n spite of the uncertainties, colIector production is increasing rapidly. Manufacturers

reported production of 426,000 m2 of collectors during the first half of 1977 (4.5 million

square feet), of which about 250,000 m

2

were low-temperature devices designed primarily for heating swimming pools. Sales

have been increasing by more than so percent every 6 months. Collector sales were

expected to amount to over $100 miIlion

during 1977.

MAJOR DESIGN CONSIDERATIONS

The enormous variety makes the selection

of an optimum collector design a complex

decision. The choice can only be made by

analyzing the space available for collectors

on building roofs or in landscaping around

buildings, the local climate (including the

availability of direct and indirect sunlight),

and the compatibility of the collector output with storage equipment, engines, and

other elements of the solar energy system.

Clearly, no single design will be optimum for

all applications in all climates. The following discussion reviews some of the major

variables which must be considered i n selecting a collector.

TRACKING VERSUS

NONTRACKING SYSTEMS

The vast majority of the collectors now on

the market do not follow or “track” the Sun

or concentrate sunlight with an optical system, but are “flat-plate” systems rigidl y

fixed to rooftops or frames in fields. This

kind of collector has the advantage of simplicity and reliability, and can be integrated

into buiIding designs with relative ease.

If sufficient land is available and large

quantities of low-temperature (500 to 90° C)

thermal energy are required, shallow pond

‘Stoll, R. (DOE) So/ar Collector Manufacturing Activity, November 1977

collectors, which use the earth for much of

their support, will almost certainly provide

the lowest cost solar energy. Nonfocusing

collectors are also uniquely able to make

use of diffuse sunlight reflected from the atmosphere and the ground. (Some diffuse

solar energy can be collected by concentrators which magnify the Sun’s intensity

only 2 to 3 times, ) Flat-plate colIectors are

not able to provide temperatures hig h

enough to operate most kinds of heat engines, however, and cannot be used to provide high-temperature process heat. (A heat

engine which can operate from the temperatures produced by flat-plate devices is discussed i n chapter IX, Energy Conversio n

With Heat Engines. )

Some types of flat-plate collectors may

cost more per unit of aperture than tracking

devices. This is because flat-plate units require a considerable amount of material for

each unit of collector area —the entire area

must be covered by an absorber surface, insulation, and one or two layers of glass or

plastic. The large heated area also means

that thermal losses for flat-plate devices are

generally larger than those of systems which

concentrate sunlight, even though the concentrating systems typically operate at higher temperatures,

Systems which track the Sun and concentrate sunlight are able to produce the high

temperatures needed to operate efficient

heat engines or can be used to reduce the

area of photovoltaic cells needed for electricity production. Their use with solar cells

is important if the cost per unit area of the

tracking collector is significantly cheaper

than the unit area celI costs, and if the tracking device allows the use of a high-efficiency cell. This is discussed in greater detail in later sections.

Although most concentrating collectors

now on the market cost considerably more

than flat-plate devices, it may eventually be

possible to build concentrating device s

which cost no more (perhaps less) than

standard fIat-plate systems since most of the

area of concentrating collectors is covered

only with a thin layer of reflective surface or
Ch. Vlll Collectors ● 2 4 7

lens material. The inability to utilize diffuse

sunlight is compensated for, to a large extent, by the fact that tracking devices can

maintain a better angle to the Sun than stationary systems.

Systems have been proposed which concentrate sunlight without tracking — examples are simple stationary reflectors placed

between tilted flat-plate collectors and the

“compound parabolic concentrator” under

development at the Argonne National Laboratory; and systems have been proposed in

which flat-plate colIectors track the Sun

without concentrating sunlight. I n most

cases, however, tracking and concentration

are used together.

Tracking collectors can be conveniently

divided into two general categories depending on whether they track the Sun by tilting

around one or two axes. The one-axis tracking systems are typicalIy shaped Iike long

troughs which swing about the trough’s long

axis. These troughs cannot keep the receiver

aperture perpendicuIar to the Sun’s direction, but provide better Sun angles than a

fixed device. One-axis systems typically are

used to magnify the Sun less than 50 times

and are not used to provide temperatures

above 3500 C (660 0 F); some simple, inexpensive systems are designed to produce

fluids at650 to 1200C(1500 to 2500 F).

The advantages of concentrating collectors are counterbalanced by the added costs

of maintaining the optical surfaces an d

moving components, and by the cost of the

tracking unit itself. The tracking systems

need not be very expensive since a single

tracker can be used to drive a large array of

colIectors and wear on the moving parts wiII

be minimal since a collector will rotate only

11,000 times in 30 years. Maintenance of the

optical surfaces is Iikely to be the largest

problem. Optical losses can be a dominant

factor in the overall efficiency of concentrating collectors (the relatively poor optical

efficiency of some concentrating collectors

tends to offset their relatively good thermal

efficiency), and these losses can be significantly increased if dirt or scratches accumulate on mirror or lens surfaces.

Dirt can scatter light and therefore interferes with the ability of the optical devices

to focus light even when the amount of light

absorbed by the dust is not important. Recent experience at Sandia Laboratories has

indicated that the specular reflectivity of

tracking mirrors can be reduced by as much

as 15 percent in poor locations if the mirrors

are not washed during a year. The effect is

very sensitive to the location of the collectors since precipitation can reduce dust accumulation but no data is available on this

problem in most locations. Table VII l-l indicates the degradation in the performance of

flat-plate photovoltaic collectors. It can be

seen that the effect of dirt depends strongly

on the cover material and the operating environment. The degradation of performance

apparently is quite rapid during the first 3

months, but levels off quickly. Performance

at 9 months is not much worse than performance at 3 months. 2 A relatively simple hosedown once or twice a year may be sufficient

for most cleaning requirements. ’ Larger collector arrays may require specially designed

equipment to faciIitate cleaning colIectors.

The timing of cleaning cycles will depend

on a detailed comparison of the cost of

alternative cleaning schedules and the cost

of energy lost because of the dirt which can

accumulate as a result of each schedule. Unfortunately, most types of tracking devices

have not operated long enough to allow the

collection of adequate information about

the degradation of performance over time.

Cleaning is, of course, also important for

flat-plate collectors, but tends not to be as

critical a factor in their performance since a

significant fraction of the light scattered by

dirt can

sorber.

Win d

problem

can act

tracking

still be captured by a flat-plate abIoads present a particularly serious

for tracking collectors since they

like sails and much of the cost o f

devices results from the need to

2A. F, Forestieri, NA5A Lewis Research Center,

private communication, November 1977

‘Rosco Champion (Sandia Laboratories), private

communication, February 1977
248 Ž Solar Technology to Today’s Energy Needs

Table Vlll-1.— Degradation in the Performance of Flat-Plate

Photovoitaic Arrays Located in Cleveland, Ohio,

September-December 1975

Heavy industrial Suburban

environment environment

81 days 250 days 74 days 250 days

Arrays not cleaned

Cells encapsulated in glass -5.7 + 1.8

Cells encapsulated in silicone rubber (average of three

products tested) -32 ~-3 0 -9

Performance after arrays

scrubbed with a detergent

solution

Cells encapsulated in glass. . . . . + 1.8 0

Cells encapsulated in silicone rubber (average of

three products tested) . . . . . . . . . -7 ~ -12 -2 -6 to -10

NOTE. Measurement error was - ~ 20/., so + 1.8% means only that no measurable degradation had OC.

curred

SOURCE Forest lerl, A F “Results of Outdoor Real Time and Accelerated Testing” presented at ERDA

National Photovoltalc Program Review, SIltcon Technology Program Branch, San Diego, Callf ,

Jan 18, 1977 (p 230)

Forestlerl, A F private communtcatlon, November 1977

build massive supporting structures capable

of withstanding high winds. A clever technique for reducing such costs would be a

welcome innovation.

Another potential problem with tracking

systems is the difficulty of integrating the

devices aesthetically into the architecture

of a building; many of the experimental

tracking systems are far from attractive. The

architectural problem of integrating tracking systems gracefully into a building, however, has not been adequately examined.

Finally, it can be difficult to design reliable couplings to carry very hot fIuids from

a moving receiver. Several approaches are

possible. For temperatures below boiling, a

flexible radiator hose may be adequate,

although occasional replacements may be

necessary. For temperatures of 4000 to 6000

F, rubberized braided-steel hose can be

used. For higher temperatures, stainless

steel accordian bellows can be used. These

are commonly used to allow for expansion

and contraction in industrial pipes which

must carry very hot or very cold fluids or

steam. The reliability of each approach can

only be established with carefuI testing.

INSTALLATION

The cost of installing collectors is an important and often overlooked component of

the cost of a solar system. The relatively

straightforward plumbing, carpentry, and

electrical work associated with installing

collectors can represent more than half of

the installed cost of a collector system.

These costs tend to be significantly higher in

the case of devices retrofitted onto existing

structures.

It may be possible to integrate collectors

into the walls or roofs of new buildings in a

way that can lead to some savings in building materials and insulation. Plumbing and

wiring costs can be minimized with careful

building designs. Some additional construction costs may be incurred if heavy collectors or collectors subject to high wind loads

must be supported by the building.
Ch. VIII Collectors ● 2 4 9

Collector systems which are not attached

to buildings incur the additional cost of

land-grading, concrete foundations, and the

cost of purchasing needed land. I n many

cases, the land cost can be eliminated by

mounting collectors over parking lots or

other areas where the colIectors will not interfere with use.

The problem of installation costs has not

received the attention which this issu e

merits.

WORKING FLUID

A variety of fluids can be used to convey

the energy from a solar collector to the site

where the energy is needed or into storage.

At low temperatures, the prime candidates

are air, water and mixtures of water, and

antifreeze. (Pure water cannot be used in

colder climates unless the system is designed to drain completely during cold, sunless periods or the collector is made from

flexible plastics or other materials which are

not damaged by expansion. )

Air collectors have the advantage o f

avoiding the problem of freezing altogether,

and are not affected by the corrosion which

can result from untreated water. Air can be

heated to temperatures above boiling without producing excessive pressures, and leaks

in air colIectors do not lead to building

damage. Air collector heating systems can

use inexpensive rock beds for heat storage,

thus eliminating the inefficiencies, temperature drops, and costs associated with heat

exchangers. However, the relatively low

density and specific heat of air (compared

to water) means that the collectors, storage,

and heat transfer systems must be considerably buIkier than the Iiqu id systems.

Water can also be used as the working

fluid in high-temperature systems, but pressurized systems can be expensive, especially

if steam must pass through rotating joints or

be transported over long distances. A variety

of heat transfer fluids have been developed

for chemical processing which can be used

to transport heat from solar collectors, although there are disadvantages associated

with their use. These fluids can be costly,

some are flammable, and others degrade

with continued thermal cycling. The use of

helium gas has been proposed for use in the

receivers of very high-temperature colIector

systems.

If an efficient and inexpensive chemical

process can be developed which either converts light directly into chemical energy

(photochemical reactions) or which uses

thermal energy to drive a chemical reaction

(thermochemical reactions), it may be possible to pump the appropriate chemicals directly into collectors to produce a higher

energy material which can be stored for

later use.

SURVIVAL IN ADVERSE CONDITIONS

A collector system should be able to withstand strong wind and hail, and should be

able to operate after snowstorms. Some

tracking collectors are designed to protect

themselves from inclement weather by turning the vulnerable surfaces down toward the

building or the ground.

Another factor which must be considered

is the collector’s ability to survive a failure

of the pump control systems or plumbing

which prevents the working fluid from carrying heat away from the collectors. If fluid

flow stops, the temperature of even simple

colIectors can reach 1000 to 1500 C (the socalled “stagnation temperature” of the Col -

lector). These temperatures can melt critical

components of poorly designed systems o r

cause expensive damage in other ways. The

colIector performance and certification

tests designed by the National Bureau of

Standards will include a test of the performance of the collector after it has operated without cooling fluids for some length

of time.

2 fl-fi42 () - 17
250 Ž Solar Technology to Today’s Energy Needs

SURVEY OF COLLECTOR DESIGN S

The following section examines a representative set of solar collectors. Some of

these devices are on the market and some

remain in the laboratory, but an attempt has

been made to represent each generic category. The selection of particular collectors

as examples does not imply any judgment

about their performance relative to other

devices, nor is the survey intended to provide a comprehensive listing of all available

designs. Extensive catalogs of solar collectors have been published by the Energy Research and Development Administratio n

(ERDA),

4 the House Subcommittee on Energy Research, Development, and Demonstration,

5 and the Solar Energy Industries Assoc i at ion. 6

“PASSIVE” SYSTEMS

The heating and cooling requirements of

buildings can be reduced if care is taken in

the design of the building and the choice of

a building site. With imaginative planning,

most of the options should not add substantially to the cost or detract from the appearance of structures. At some added cost, new

buildings can be designed with more elaborate structural features (such as large southfacing windows and thick walls) which can

further reduce heating and cooling requirements. These features are all commonly categorized as “passive solar” collection systems since they typically have no moving

parts.

Passive systems are extremely attractive

because of their simplicity, very low initial

cost, and freedom from maintenance costs.

‘Catalog on Solar Energy Heating and Cooling Products. ERDA-75 ERDA Technical Information Center,

Oak Ridge, October 1975

‘Survey of Solar Energy Products and Services –

May 1975. Prepared for the Subcommittee on Energy

Research, Development, and Demonstration, U.S.

House of Representatives, by the Congressional

Research Service, Library of Congress, June 1975 For

sale by U S Government Printing Office, $460

‘So/ar /ndustry Index. Solar Energy Industrie s

Association, January 1977 $800 prepaid

Many of the more sophisticated passive

solar designs are only applicable to new

construction since they affect the basic design of the building; many simple changes,

such as the addition of awnings, shutters,

and lean-to greenhouses can be retrofit on

existing structures. Temperature control can

also be difficuIt with some systems.

Siting

A wise decision about building placement

should take into account local topography,

sun angles, trees and other vegetation ,

ground water, precipitation patterns, and

other aspects of the local climate and geography. There cannot be a simple, all-inclusive formula for resolving these issues because each decision must be made on the

basis of specific site conditions. Table VI II-2

indicates some of the basic elements of

building siting decisions for four different

climatic regions, and figure VII l-l gives an

example of an efficient siting plan developed by the AlA Research Corporation. The

following features were used in developing

the plan: 7

●

●

●

●

●

●

✎

The use of windbreak planting;

The orientation of road alinement with

planting on either side to channel summer breezes;

The location of units in a configuration

suggested by the topography;

The use of the garage to buffer the

dwelling from northwest winter winds;

The use of berms to shelter outdoor Iiving terraces; and

The use and location of deciduous trees

to block or filter afternoon sunlight in

the summer.

‘The American I nstltute of Architects Research Corporation, Solar Dwelling Design Concepts, prepared

for the U S Department of Housing and Urban

Development, Office of Policy Development and

Research, May 1976
Ch. V/// Collectors

Table VI II-2.—Site Orientation Chart

Type of climate coo l Temperate Hot humid Hot arid

Adaptations

Position on slope

Orientation on slope

Relation to water

Preferred winds

Clustering

Building orientation ●

Tree forms

Road orientation

Materials coloration

Maximize warming

effects of solar

radiation. Reduce

impact of winter wind

Avoid local climatlc

cold pockets

Low for wind shelter

South to southeast

Near large body of

water

Sheltered from north

and west

Around Sun pockets

Southeast

Deciduous trees near

building; evergreens

for windbreaks

Crosswise to winter

wind

Medium to dark

Maximize warming

effects of Sun in

winter. Maximize

shade in summer.

Reduce impact of

winter wind but

allow air circuIatlon

in summer

Middle-upper for solar

radiation exposure

South to southeast

Close to water, but

avoid coastal fog

Avoid continental

cold winds

Around a common,

sunny terrace

South to southeast

Deciduous trees nearby

on west; no evergreens

near on south

Crosswise to winter

wind

Medium

SOURCE Solar Dwelhng Destgn Concepts op clt p 72

In warmer climates, a building should be

placed at the highest part of the terrain to

take advantage of cooling winds (a form of

solar energy); in colder climates, it should be

located, ideally, in the cup of a hill, allowing

sunlight to reach the buiIding whiIe protecting it from chilling winds.

When the terrain and local building codes

permit, siting at least part of the building

underground or at ground level provides excellent insulation. Trees are also an important factor in site selection, acting both as a

windbreaker and a Iightbreaker. Deciduous

trees shade the south side of the house for

much of the year, alIowing sun Iight to penetrate during the colder months. The same

shading principle is true of such plants as ivy

on the walIs of the house,

Maximize shade

Maximize wind

High for wind

South

Near any water

Sheltered from north

Open to wind

South, toward prevailing wind

High canopy trees;

use deciduous trees

near buiIding

Broad channel; E-W

axis

Light, especially

for roof

Maximize shade late

morning and all afternoon. Maximize humidity,

Maximize air movement

in summer

Low for cool alr flow

East-southeast for p.m

shade

On lee side of water

Exposed to prevailIng

winds

Along E-W axis, for

shade and wind

South

Trees overhanging

roof if possible

Narrow; E-W axis

Light on exposed surfaces, dark to avoid

refIect ion

—

Basic Architectural Considerations

A considerable amount of passive solar

heating and cooling can be achieved simply

by carefully designing the shape of a house,

and the placement of windows and thermal

masses in the building (e. g., thick masonr y

walls). Many older buildings incorporated

these features in their designs. (The art of

taking such factors into consideration in designing a house seems to have been neglected when inexpensive heating fuels became available. )

The size and location of windows is a major factor in determining the temperature of

a house. Large, south-facing windows can

collect a surprising amount of solar heat,

which is transferred to walIs and floors.
252 ● Solar Technology to Today’s Energy Needs

Figure VII I-I .—A Sample Site Plan Illustrating Techniques

for Minimizing Heating and Cooling Requirements

SOURCE The AlA Research Corporation, “Solar Dwelllng Design Concepts”
Small, northern windows minimize heat loss.

The use of natural shading and orientation

to breeze s provides i m proved cooling

through windows.

The basic shape of a structure is also important. Long ranch-style homes, for example, require much more heating per unit of

floor space than cube-shaped, two-story

homes, Roof overhangs should shade windows during the summer when the Sun is

high in the sky and allow sunlight to enter

when the Sun is lower in the sky during the

winter months. Dense interior materials with

a high heat-retaining capacity, such as masonry, concrete, or stone, can be used to absorb surplus heat from sunlight during the

day, and return this heat to the room after

dark.

Passive heating and cooling of buildings

can be enhanced by taking advantage of the

heat gained in southern walls and roofs,

natural convection, and the heat-storage

capabilities inherent in windows and walls.

A number of recent publications have reviewed these designs. 8 9 10

The simplest systems consist only of a

window with insulated shutters. The shutters

are opened to permit sunlight to enter and

heat the house during winter days, and are

closed at night to prevent heat from escaping. The shutters are closed during summer

days because white or silver surfaces on

their outer surface reflect the Sun’s heat.

During summer nights, the units open to

cool the building. Several innovative techniques have been developed for controlling

shutters and covers of this kind. Buildings

have been designed which incorporat e

greenhouses into the southern wall. Designers of one such system, located on

‘B Anderson, (Total E nvlronmental Action), The

\o/ar tfome t?ook, Cheshire Hooks, Church H Ill, Harrlsvllle, N H 1976

‘Leek IC, et al , Other Homes and Garbage lle~l~n~

tor Se/f-Sufflclent L/\T/rrg, Sierra C I ub Books, 1975

‘”10$ Alamos Sc Ientiflc Laboratory F’assi~e Solar

Heating and Cooling Conference and Workshop Proceedings, LA-6637-C, May 18-19, 1976

1‘ Bruce Anderson, Solar Energ} I undarnentals In

Bulldlrrg De\/gn.

prince Edward

their building re

Ch. Vlll Co//ectors ● 2 5 3

Island, Canada, claim that

mained at a comfortable

temperature throughout the severe winter of

1976-77 without using backup heating systems. 2

Two slightly more elaborate techniques

involve the use of “thermosyphoning” and

thermal masses. The “thermosyphoning ”

systems use natural or forced convection to

heat building air in walls, ceilings, or window surfaces heated by the Sun. 1

3 A variety

of techniques have used solar radiation for

heating a mass with large heat capacity via

sunlight, and using direct radiant heating

from these masses after the Sun sets. The

thermal mass can be nothing more than a

dark wall or floor made of thick masonry,

stone, or adobe, or a water tank integrated

into the wall or floor. The system designed

by Steve Baer of the Zomeworks Corporation uses cylinders of water to provide the

thermal mass. 1

5

A system which has become known as the

“Trombe-wall” collecto r (after Feli x

Trombe, a French designer who has designed

several such structures since 1967) is illustrated in figure VII I-2. Figure VII I-3 shows

a house in Maryland which includes a

Trombe wall, The owners estimate that the

passive solar system added approximately

$2,500 to their construction costs. The device is expected to provide about 50 percent

of the building’s heat requirements.

The Trombe wall is essentially a vertical

hot air collector which uses a thick wal l

both for a receiver and a storage system.

The air can circulate with natural convection or with a fan. In most climates, the performance of the system is improved if adjustable vents are installed over the open12J Todd, et al , The )ourn,q} of th~ ,h’~b{ 4/chemists,

New Alchem}, Woods Hole, Mass , spring 1975

‘‘T Price, ‘‘Low-Tee h no logy Solar Homes that

work ~vlth Natll re, ” Popu/ar Science, TI mes Mirror

Magaz Ines, I nc , December 1976, pp 95-98, 143

14S F3aer, Sunspot~, The Zomeworks Corporatio n

(1975)

) ‘A4 J H arisen, “The Bened Ictlne Monastery, ” So/ar

Age, October 1977, p 24
254 ● Solar Technology to Today’s Energy Needs

Figure Vlll-2.—The Operation of the

Trombe-Wall Collector/Storage System

(Sun

Solar

heated

air

heat : Transparent cover

.

.

ings which connect the collector airspace

with the interior of the house.

16

The response of walls of various thickness

is illustrated in figure VI I I-4, The ability of

the thermal mass to average the external

temperatures is clearly illustrated. Analysis

of the many varients of this system which

are possible have just begun, and an analysis

of the economics of the systems is difficult

because of the scarcity of consistent cost information and the small number of systems

which have been adequately instrumented.

The “Skytherm ” house in Atascadero,

Cal if., uses water beds covered by remov -

able insulating panels on the roof of a building. During the winter, the panels are automatically removed during the day, allowing

the water to be heated and replaced at

night. Heat is provided to the living areas by

direct radiation through a metal ceiling

“J D Balcomb, et al , “Thermal Storage Walls for

Passive Solar Heating Evaluated, ” Solar Age, August

1977, p 22

Figure VII I-3.—A House Using a Trombe-Wall Collector Located in Eastern Maryland

PHOTO Courtesy of Andrew M Shapiro, “The Crosley’s House—With Calculations and Results,” So/ar Age, November 1977, p 31
Days

I I 1 I 1

31 1 2 3 4 5 6 7

Days

2345 6

Days

SOURCE Balcomb, et al SImu Iat I(JII Analy 51s 1,f Passive Sol,)r Heat(Id Bulldir]qs -- Prf,limlnary resu Its So/a( En erg j , I )1 19 ( 1977 I I 1,if,+. 281

separating the interior of the house from the

water beds. I n dry climates with cool summer nights, the system can also provide

cooling. Heat is radiated from the water to

the sky during the night when the insulating

covers are removed, and the thermal mass is

used to absorb building heat during the day

when the insulating covers are i n place. 7 I n

some recent measurements, this house was

shown to maintain an inside temperature between 180 and 240 C (65 0 and 750 F) during

i ‘H a rold Hay, privdte comrnu nlcdt Ion

a 9-month period in which the average high

temperature for the hottest month was 32°

C (90 0 F) and the average low temperature

for the coldest month was -1°C (30 0 F).

18

STATIONARY FLAT-PLATE COLLECTORS

Flat-plate collectors have been used for

several decades to provide hot water in

‘8Phl I Ip W B Miles, “Thernlal Evaluation of a

House U$i ng a Movable I nsu Iatlon Heating and Cooling Syjtem, ” So/ar Energy, Vol 18, (1 976)
256 ● Solar Technology to Today’s Energy Needs

Australia, Japan, and Israel. Large numbers

of the devices were also sold in southern

parts of the United States during the late

1920’s and early 1930’s, but sales declined

rapidly as low-cost natural gas and oiI became available. I n recent years, however,

there has been a great resurgence of interest

in the systems, and a large number of designs are being marketed or prepared for

marketing. A typical installation is shown in

figure VI 11-5.

The cross section of a typical collector is

shown in figure VI 11-6. The fluid is heated as

it is passed over or through an absorbing surface. At some additional expense, this surface can be specially designed to maximize

the amount of sunlight it absorbs and to

minimize its radiation at the operating temperature of the collector. The absorptivity

of the system is high for wavelengths where

the Sun’s intensity is greatest and low at

wavelengths where the intensity of the radiation from the heated receiver surface is

greatest, A number of such “selective surfaces” are now on the market but the development of a high-performance, low-cost selective surface would be a great boon to the

colIector industry.

The heated surfaces are insulated on the

back and sides by standard types of insulation (e. g., fiberglass), and on the front by one

or two layers of glass or plastic. These transparent or semitransparent covers can also

be made selective. Several common materials are nearly transparent to visible light

from the Sun but absorb the infrared radiFigure Vlll-5.— Typical Home With Solar Water Heating Using Flat-Plate Collectors

--, 

PHOTO Courtesy of American Hellothermal Corp
Ch. VIII Collectors ● 2 5 7

Figure Vlll-6.— Cross-Section of a Typical Modular

Flat-Plate Solar Collector

ated by the colIectors. (AlI common glass

possesses this property. This is the basis of

the “greenhouse effect” which heats closed

cars and rooms with southern windows. )

Special “heat mirror coatings, ” such as indium oxide, can be deposited on collector

covers to further reduce losses Such coatings reflect the infrared radiated by the hot

receiver, but permit most of the incident

sunlight to pass into the collector.

Pond Collectors

Pond collectors can be used when sufficient level ground is available near a site

where relatively low-temperature flu ids are

required; the systems will probably be most

useful when combined with long-term (6-

month) thermal storage or when used for industrial-processing facilities since very little

output is provided during winter months. Research on these devices has been conducted

in Israel for many years. One of the first installations in the United States using such

collectors was designed by the SOHIO oil

company working with the Lawrence Livermore Laboratory to develop a pond system

which could be used for processing uranium. Two types of solar pond collectors are

shown in figure VIII-7a and VIIl-7b.

The basic Livermore collector design consists of a reinforced concrete curb which

forms the periphery of the pond. A layer of

sand and a layer of foam-glass insulation are

placed inside this curb and a watertight

polyvinyl chloride (PVC) bag is placed on top

of the rigid insulation. The upper cover of

this bag consists of 12 mill (C).3 mm) clear

PVC while the bottom layer is a 30 mill

(0.8mm) black PVC. A single upper cover for

the collector is provided by a flexible fiberglass material called Filon which is commonly used to construct greenhouses. The

Figure VIIl-7a.— Pond Collector With a Rigid Cover

PHOTO Courtesy of University of Call fornta, Lawrence Llvermore Laboratory and the U S Department of Energy
258 ● Solar Technology to Today’s Energy Needs

1.

2,

3.

4.

5.

6.

7.

8.

9,

Polyvinylchloride Pool Liner

Solar Reflector (North Side)

Outer Glazing of Collector

Collector absorber Surface and Inner Glazing

Bead Insulation

Earth Berm

Pool Water

Pool Extension Wall

Support Structure

Source J Taylor Beard, Ibid

entire collector is inclined to provide a slope

of 0.083 percent (1 inch in 100 feet) of collector length. One I imitation of this design is

that the thin PVC bag probably must be replaced every 5 years. It is estimated that this

replacement wilI cost about $6/m2 of collector.

1 9

A contracting firm in New Mexico has

estimated that an 8,000 m2 colIector based

on this design could be constructed for

about $30/ m

2

.

20 (Smaller systems would ,

however, be considerably more expensive

per unit area.) This collector is typically

operated by filling the bag with water in the

morning and draining the heated water in

the evening, instead of flowing water continuously through the collector. It would be

able to provide fluids at a temperature of

about sO 0 to 600 C during the summer and

about 300 to 350 C on sunny winter days, If

a second cover is added to the collector (at

a probable cost of less than $5/m

2

) the

19Alan Casamajor, Lawrence Livermore Laboratory,

private communication, November 1977

ZOl bld

devices should be able to provide fluids at

about 900 C. PVC bags could not be used at

these temperatures, however.

A number of improvements to this basic

design are being investigated. The TeledyneBrown Company has proposed replacing the

concrete curbing with an extruded aluminum frame which could be assemble d

rapidly on simple footings. This desig n

would also permit rapid replacement of the

plastic film materials. 21 A number of plastic

materials are being examined which would

improve on the performance of the PVC

systems used in the experimental systems.

Polybutylene (which is used for “boil in the

bag” processed foods) can be extruded into

a thin (5 mill 0.1 mm) bag, saving material

costs and permitting operation at higher

temperatures. A du Pont plastic calle d

Hypalon can be used to provide a back absorbing surface for the collector whic h

would probably last 10 to 20 years.

‘][lr Gerald Guinn, Teledyne-Brown Company,

private communication, November 1977.
Ch. VIII Co//ectors ● 2 5 9

Two systems which use a pond collector

combined with a thermal storage pond have

been built and are currently being tested in

Virginia

22 23 (figure VI II-7). In one design, the

storage system is simply a trough in the

ground lined with a plastic swimming pool

liner, The trough is filled with water and

covered with a foot of styrofoam beads to

provide insulation. The thermal losses from

such a pond should be acceptable, even

without insulation under the pond. The collector is a modified Thomason trickle collector placed over the floating beads. The

top cover is a fIexible plastic (Monsanto 602)

supported by air pressure from a smal l

blower. The pond uses a reflector along the

north side to enhance its performance.

A similar, but somewhat larger pond collector/storage system (1 ,340 ft

2

, 80,00 0

gallons) has been built to heat a wellinsuIated 5,000 ft

2 home in StanardsvilIe,

V a .

24 This system, which cost $6,000, is expected to provide all of the heating needs of

the house. A unique radiant heating system

is used which permits the use of water only

50 to 100 F warmer than the room temperature for heating purposes.

Pond collectors provide a smaller fraction

of their output during winter months than

tilted collectors since the winter Sun is low

in the sky. For conditions typical of many

solar heating systems, the output occurring

during the coldest 6 months of the year is

only 5 to 16 percent of the total annual output. (See table VII 1-13 at the end of this

chapter. ) As a result, the attractiveness of

ponds used for heating would be greatly increased if a low-cost technique for storing

energy generated by the pond during the

summer is developed. It is possible to build

the colIector on top of a pond.

‘2] Taylor Beard, F A Iachetta, L V Lllleleht, an d

~ W Dickey, Annual Co//ect/on and Storage of So/ar

Energy for the Ffeat/ng of Elu//dings, A nnua/ Progress

Report, May 1976-J uly 1977 to ERDA under Contract

No E-(40-1 }51 36, Publl( ation ORO,’51 36-77

‘‘john W Dickey, “Total Solar Heat-Totally Nonpolluting, ” presented at E Ieventh Advanced Seminar,

Society for Cllnlcal Ecology, San Francisco, Callf ,

Oct 31, 1977

“John W Dickey, Ibid

Flat-Plate Collectors Assembled Onsite

Thomason.–One of the oldest and simplest

solar liquid collector designs used for heating buiIdings is the “Solaris ” system designed by Harry E. Thomason. The first system was installed in a suburb of Washington, D. C., in 1959. In this system, water is

pumped to the roof ridge and trickled down

channels of a black-painted, corrugatedaluminum absorber. The heated water is collected in a gutter at the cave. A single glass

cover is used. The system can only produce

fluids with temperatures in the range of 300

to 500 C. Special ductwork is required in the

houses employing the system, since relatively large amounts of air must be moved

through the house; the air used to heat the

house is cooler than air typically used in

forced-air heating systems. Systems are sold

with a 5-year guarantee. The performance of

the system has been a subject of continuous

controversy.

Calmac.–Another low-priced collector is

the Calmac Sunmat. The absorber consists

of a 4-foot-wide mat of black synthetic rubber tubes. At the building site, the mat is

spread on l-inch-thick fiberglass insulation

board and glazed over with translucen t

pIastic/fiberglass sheets. The Sunmat’s nonmetallic materials have been tested up to

180° C, and the price of materials fo r

double-glazed systems is $35 to $44/m

2

.

Assembling the system will, of course, add

significantly to syste m costs, but th e

assembly is simple enough that unskilled

workers or homeowners couId do it. The Iife

expectancy of the system remains to be

established.

Factory-Assembled Modular Collectors

PPG.-Glass has been used longer than

plastic as a flat-plate cover material, and

PPG built its Baseline Solar Collecto r

around standard, hermetically sealed ,

double-pane window units. PPG’s collector

consists of a flat, black, aluminum roll-bond

absorber backed by 6 cm of fiberglass insulation. Panels are 193 by 87 by 9.5 cm

(76-3/16 by 34-3/16 by 3-3/4 in) and weigh 50

kg (110 Ibs) empty. They are available only
. -

260 ● Solar Technology to Today’s Energy Needs

through distributors and contractors. PPG

recommends that the collectors be used in a

closed system with treated water to prevent

corrosion. Collectors are sold with a 2-year

warranty which excludes glass breakage.

(Although the insulation is optional, that option has been assumed in the cost shown in

the summary table at the end of this chapter. Other options include copper roll-bond

absorbers, selective surface, and singlecover

glass.)

Sunworks.–Sunworks sells a selective-surface collector with a single glass cover for

$84 to $114/m2. This design can achieve efficiencies comparable to those of doublecover systems which do not use selective

surfaces. The absorber is copper tubing

soldered to a copper sheet and treated to

produce a selective surface. Because it is

copper, a tapwater, flow-through system can

be used. Panels measure 91 by 213 by 10 cm

(4 ft by 7 ft by 4 in), and weigh 50 kg (110 Ibs)

empty. A 5-year warranty is offered, excluding cover-glass breakage.

Honeywell/Lennox.–Where output temperatures of 950 C and higher are required,

higher efficiency can be achieved if a selective-surfaced absorber is combined with two

covers. Lennox Industries markets a collector of this type under license from Honeywell for around $145/m2 wholesale. Two

sheets of antireflection-etc heal, low-iron

glass, and a black-chrome selective coating

on the steel absorber are key features of the

high-performance Honeywell LSC-18-I Solar

Collector. Copper tubing, bonded to the

steel plate, provides the resistance of copper to fluid corrosion without the expense of

an all-copper system.

Panel dimensions are 183 by 91 by 16.5

cm (6 ft by 3 ft by 6-1/2 in) and dry weight is

68 kg(150 Ibs).

Solaron.-The Solaron collector is an airheating device designed by George Lof, who

has been designing solar collectors f o r

nearly 30 years. The device (shown in figure

VI 11-8) has a steel frame insulated with 3.75

Figure VII I-8.—Typical Air Collector Installation

SOURCE Solaron Inc Air to the collector
in (9.5 cm) fiberglass and has

Ch. VIII Co//ectors ● 261

two 0.125 in

(0.32 cm) low-iron, tempered-glass covers.

The absorber is a 28-gauge steel plate with a

high-absorbance ceramic enamel coating.

The collector is about 65-percent efficient

when the temperature of the air leaving the

colIector is 490 C above the ambient a i r

temperature. 25 The company has attempted

to make the collector easy to install by

designing units so that they can be butted

together and bolted in place without additional fittings between collectors, Th e

wholesale price of the device is currently

$1 18/m2. 2’

TUBULAR SOLAR COLLECTORS

Another type of stationary collector beginning to reach the market has a tubular

rather than flat-plate configuration. T h e

heat-transfer fluid is circulated through a

glass or metal tube which is enclosed in a

larger glass tube The space between the inner and outer tubes is dead air or a vacuum,

If a vacuum is combined with a selective

surface, thermal losses are much smaller

than with the conventional f tat-plate design.

The tubular concept also eliminates insulation in back of the absorber. Such a collector can be lighter than the conventional

double-glazed, fIat-plate type,

The outer glass envelope is produced by

the same machines which make fIuorescentIighting tubes. Indeed, three of the four

manufacturers of tubuIar colIectors are also

major makers of tubular lamps. The fourth,

KTA, is a small business which buys its tubing from a large fIuorescent Iight tube manufacturer.

Each manufacturer boosts its collector’s

performance differently (figure VI 11-9). Philips of the Netherlands and KTA silver the

bottom half of the glass tube. Owens-1 Illinois

spaces the tubes and places a flat, white

refIector behind them. General EIectric also

2 ‘The Solaron Corporation, 485001 Ive Street, Conlmerce City, Colo 80022, “Technical Data, Selres 2000

Alr Type Solar Col Iector ”

“George Lof, Solaron Corporation, private communlcatlon, November 1977

spaces the tubes, but puts a reflectiv e

trough behind them. KTA does not evacuate

the outer-glass tube, but covers the array of

tubes with a plexiglass cover which serves

both to reduce heat losses and protect the

tubes. Owens-1 Ilinois, KTA, and General

Electric apply a selective surface to the absorber while Philips applies a selective heat

mirror of indium oxide to the outer-glass

tube.

CONCENTRATING COLLECTORS

Nontracking Concentrating Systems

Boosted Flat Plates.–The simplest concentrator is the boosted flat-plate collector.

One or more flat mirrors are mounted so

that they reflect light onto a flat-plate collector most of the time. The rows of collectors run east to west and the mirrors are between the rows, In winter, when the Sun is

low in the sky, the light comes straight into

the collectors, missing the mirrors. I n sum -

mer, when higher temperatures are needed

to operate absorption air-conditioning, the

Sun is higher in the sky and strikes both the

collector and the mirrors — thus increasing

the concentration of Iight on the colIector.

Several varients on this basic approach

have been proposed, Some of the tubular

collectors, shown in figure VIII-10, for example, use a stationary or cusp-shaped mirror

to achieve a low level of concentration. A

system proposed by K. Celchuck of JPL uses

a shaped-mirror unit mounted between stationary flat plates, The mirror unit is manually I if ted and rotated twice a year to ensure maximum performance during the summer and winter seasons

Several recent theoretical and experimental studies of the performance of simple

mirror booster systems have indicated that

the output Of flat-plate collectors can be enhanced by factors of 1.45 to 1.6.2728

2 7A M Clauslng and A L Edgecombe, “Solar Collector Cost Reduction with Reflector Enhancement, ”

ISES 1977 meeting, p 37-25

“R L. Reid, et al , “Measurements on the Effect of

Planar Reflectors on the Flux Received by Flat-Plate

Collectors,” ISES 1977 conference, p 37-12
262 ● Solar Technology to Today’s Energy Needs

Figure VlIl-9.— Various Tubular Collector Designs

Philips

Proposed optimum cusp designs (J. D, Garrison)

0

, /

/

Solar

rays

Corning Glass

SOURCES Manufacturers data

Garrison, J D ‘Optlmlzatlon of a Fixed Solar Thermal Energy Collector, ” Proceedings of the 1977 Annual Meeting

of the American SectIon of the International Solar Energy Society, Orlando Florida. June 6-10 1977, p 36-15

Ortabasl, U and W M Buehl, ‘<An Internal Cusp Reflector for an Evacuated Tubular Heat Pipe Solar Thermal Collector, 1977 ISES meeting, p 36-30
Ch. VIII Collectors ● 26.3

—

Figure Vlll-10.— Flat-Plate Collectors

With Stationary Boosters

Prepared by OTA from data below

0.5

04

0.3

0.2

1 . Collector with no reflector

Total-Internal Reflection Concentrator.–A

concentrator system using a plastic doped

with fIuorescent dies has recently been suggested which may be able to achieve concentrations on the order of 100 x with no

tracking .

29 30 The dye molecule reradiates

light that it absorbs at a random angle. The

reradiated Iight striking the receiving sur -

face at an angle greater than the angle o f

total internal reflection continues to b e

reflected until it reaches the edge of th e

sheet covered with the receiver. (The frequency of the reradiated light can be selected to optimize photovoltaic cell performance.) If the dye has zero absorptivity

at the reradiated frequencies, collection ef29W H Weber and ] Ldmbe, Appl Opt 16, 229 9

{1 976)

‘“A Goetzberger and W Breubel, Appl Phys 14, 121

(1977)

ficiencies as high as 60 to 75 percent are

theoreticalIy possible using plexiglass cells 1

to 2 meters on a side,31

Compound Parabolic Collectors.-The Compound Parabolic Concentrator (C PC) collector (also called the “Winston” or “Baranov”

collector) consists of a stationary refIective

trough with a receiver at the bottom Each

wall is a section of a parabola, and the

system is designed so that all of the light

received from a relatively large region of the

sky will reach the receiver surface (see

figure VI 11-11). Sunlight received from a

solar disk which is not on the main axis of

the collector, however, produces a very irregular image on the receiver and some care

must be taken to ensure that this lack of uniform illumination does not create damage

to the receiver. Systems with concentration

ratios of 9 to 10 can be designed which are

able to collect energy from the Sun’s disk

for at least 7 hours each day with only 10

position adjustments per year.

32 If the system is not seasonally adjusted, useful output will be available for less than 7 hours. (A

two-dimensional concentrating system has

also been designed, but this system must be

moved at 15-minute intervals about one axis

to follow the Sun during the day. ) The mirror

shape developed for this design can also be

used at the focus of other concentrating systems to reduce the requirements for hightracking precision.

The CPC cuts costs by eliminating the

need for elaborate tracking systems, but it

uses more mirror area than a trough or dish

of the same aperture because of the steep

angles of its reflective sides. The CPC also

uses more receiver pipes because of its

lower concentration ratio. Moreover, multiple reflections inside the collector can attenuate the sunlight before it reaches the

receiver, These factors considerab l

y i n -

crease the cost of the CPC design. inexpensive techniques have been proposed for producing the required shape by extrusion or

other shaping processes. Material costs of

$5 to $20/m2 appear possible for collectors

‘lA Goetzberger, op clt

“Argonne, op clt
264 ● Solar Technology to Today’s Energy Needs

Figure VII I-I 1.—One-Axis Compound Parabolic Collector

used with photovoltaic systems. Fabricating

costs are difficuit to estimate at this point.

Active Tracking and Concentrating Systems

Techniques used to track the Sun fall into

three broad categories:

1. Systems in which the concentrator and

2

the receiver both rotate (focusing can

be by means of a curved or segmented

mirror or a Fresnel lens);

Systems in which the concentrating mirrors remain stationary and the receiver

shifts to follow a moving focal point or

line; and

3 Heliostat systems in which the mirrors

rotate to focus light onto a stationary

receiver.

ONE-AXIS TRACKING

One-axis tracking collectors concentrate

the Sun’s energy onto a I i near receiver. They

typically are capable of producing temperatures in the range of 1500 to 3000 C, and

there are many different ingenious designs.

One-axis trackers can either follow the Sun

from east to west each day, or they can face

due south and tilt up-and-down to follow the

Sun. The terminology can be confusing because the axis of the east-to-west tracker

runs i n a north-to-south Iine, and the axis of

the south-facing collector runs in an east-towest line, Solar technologists usualIy refer

to these collectors according to their axis

orientations. Thus, for example, a parabolic

trough concentrator which follows the Sun

from east to west is called a “north-south
Ch. Vlll Collectors ● 26.5

Figure VIII-12. —Albuquerque-Western Tracking Collectors Installed on Modular Home

. .

trough, ” The “north-to-south” polar-mount

collectors collect more energy than northsouth or east-west troughs with horizontal

axes

Collector and Receiver—Both Tracking

Parabolic Troughs.–AIbuquerque- Western:

Albuquerque-Western Industries, a modular

housebuilder, is now producing parabolic

trough solar collectors as well as complete

solar heating and water heating systems.

The company has installed systems on new

modular houses (figure V I I l-l 2) and on existing conventional residences. The collectors (including tracker) sell for $48 to $51 per

square meter of aperture. This makes them

less expensive than most flat-plate collectors Each trough is 51 cm wide and 2.44 m

long (20 in by 8 ft) with a clear Tedlar plastic

front window and a 3.2 cm (1 ,25 in) flatblack copper absorber tube inside Th e

reflector is aluminized Mylar. The present

unpressurized system is designed to produce

hot water at up to 880°C , AlbuquerqueWestern Industries is working on an improved but more expensive collector which

wilI produce 1500 C, enough to run absorption air-conditioning or to store more heat

for winter heating, The Mylar reflector may

have a relatively short life, and a new

material may need to be developed; but

.’ ? - , 1.! r ) - 1,4

PHOTO Courtesy of Albuquerque Western Solar Industries

they are designed for easy replacement onsite.

Sandia: As part of its total energy pro -

gram, Sandia Laboratories in Albuquerque

has built some high-performance parabolic

troughs for use at 2300 to 3150 C. Sandia’s

units, Iike most other Iinear-focus colIectors,

may be mounted with the axis oriente d

either east-west or north-south. The receiver

is a selectively coated pipe inside an evacuatd glass tube. The cost of the system in

commerciaI production has not been established.

Acurex: Acurex Corporation is commercialIy producing two models of parabolic

troughs. One is a high-performance parabolic trough similar to the Sandia design

(figure VllI-13). The trough is formed by

clamping polished aluminu m refIective

sheets to parabolic ribs. The sheets are easily replaceable and the units CO I lapse for

compact shipping. Black chrome selective

coating is used on the 3,35 cm (1.3 in)

diameter stainless steel absorber pipe which

is inside a 5.08 cm (2 in) diameter glass tube

(not evacuated). The absorber tube is specially designed to increase heat transfer to

the flu id. Each trough is 3.05 meters long

and 1.83 meters wide (10 by 6 ft), and eight

troughs (end-to-end) can be driven by each
266 ● Solar Technology to Today’s Energy Needs

Figure VIII-13.—Acurex Parabolic Trough

Shadow Band Tracker Reflecting Lighting Sheet

Absorbing Receiver Tube

tracker unit. The receiver pipes of the eight

collectors attach directly to one another,

eliminating much interconnect piping and

reflector end losses. The other trough design

is basically similar but is designed for use at

lower temperatures (less than 1800 C). It is

only 4 feet wide and the absorber tube is uncovered. In a recent contract, Acurex sold

625 m2 of its collectors to New Mexico State

University for $156/m2.

Solartec: Solartec Corporation is producing a 44X concentration parabolic trough

which heats pressurized water or othe r

fluids to over 200° C. Each 1.22 by 3.05 m (4

by 10 ft) trough has an aperture of 3,4 m2

and weighs 25 kg. The 2.54 cm (1 in) hard

copper absorber pipe has a selective coating. A smaller pipe within the absorber pipe

improves fluid heat transfer by increasing

the flow velocity, The mirror is presently

Mot;r Drive

PHOTO Courtesy of Acurex Corporation, 1977

coated, anodized, polished sheet aluminum,

but other material may be used in the future

to achieve better reflectivity. There is a 2-,

5-, and 10-year limited warranty on moving

parts, reflectors, absorbers, and framework,

respectively.

Beam Engineering: Beam Engineerin g

makes a sheet aluminum parabolic trough

very simiIar to the Albuquerque-Western

trough, except that each Beam trough is

smaller and has its own tracker (figur e

VI 11-14). Costs are considerably higher but

Beam feels that large orders and the use of

fewer trackers could lower prices significantly. Each collector is 1.83 m long and

0.51 m wide (6 ft by 20 in) with a replaceable

clear Tedlar front window and a 5.08 cm (2

in) black-copper absorber tube.

Linear Fresnel Lens.–A linear Fresnel lens of

extruded acrylic plastic forms the focusing
Ch. VIII Collectors ● 2 6 7

Figure Vlll-14.— Beam Engineering Parabolic Trough on a Polar Mount

element of the Northrup concentrating solar

collector shown in figure VII 1-15. Northrup

Inc., a Texas Company whose principal business has been manufacturing heating and

cooling products , has invested nearl y

$250,000 developing this unit. Several large

DOE-assisted demonstration projects are using Northrup collectors. Each unit is 3.05 m

long with a 30.5 cm wide aperture (10 ft by

12 in). The recommended mounting is with

the axis parallel to the Earth’s axis (“polar

mount”) and with a center-to-center spacing

of 60 to 75 cm between adjacent units. One

tracker drives 24 units. Northrup offers a

limited warranty on all parts and workmanship of 18 months from shipment or 12

months from instalIation, whichever occurs

first. Currently, the collectors are muc h

more expensive than flat-plate device s

capable of producing energy at equivalent

rates,

Northrup is also working on a higher performance linear Fresnel collector with a

greater concentration ratio and a more effiPHOTO Courtesy of Beam Englneenng

cient absorber. This advanced unit will produce the higher temperatures necessary for

efficient absorption air-conditioning and

heat engine operation.

McDonnell-Douglas Company has developed several prototype high-performance

linear Fresnel collectors under contract to

the DOE/Sandia Solar Total Energy Program. Using Therminol heat-transfer fluid,

the units have produced 3150 C steam. The

3.8-cm- (1 ‘A-in) wide absorber tube is coated

with a black-chrome selective surface and

placed in a glass tube to cut heat loss (figure

VIII-16). The collector design is still being

developed. The lenses used are manufactured by Swedlow, Inc. 33 The lenses used in

the prototype were cast in one 94 by 233 cm

(37 by 92 in) piece and produced a concentration ratio of 21:1 Swedlow believes that

40:1 is about

‘‘W R Lee

Marketing Vice

Nov 17, 1976

the maximum practical limit

(Swedlow, lnc , Staff As$lstant,

President), private communication,
268 ● Solar Technology to Today’s Energy Needs

Figure VIII-15 .—(a) The Linear Fresnel Lens

and the Absorber Tube are Both Visible in

This Cross-Sectional End-View

of the Northrup Concentrating Collector

(b) Array of Northrup Collectors is Mounted

for Polar Tracking

PHOTOS Courtesy of Northrup, Inc

for linear Fresnel lens concentration. More

information on the Swedlow cast-acrylic

Fresnel lens is presented in the discussion of

two-axis, full-tracking systems.

Tracking Receiver—Stationary Mirrors

These designs give the benefits of concentration while keeping most of the collector

area stationary. But since the aperture does

not follow the Sun, early morning and late

afternoon performance suffers.

Figure Vlll-16.— Receiver Pipe Inside

McDonnell Douglas Prototype Linear

Fresnel Lens Concentrator

PHOTO: Courtesy of McDonnell Douglas Astronaut~cs Co

General Atomic.–General Atomic Company has patented a design for a trough consisting of reflective strips which can be rigidly fixed while still maintaining sharp focus

(figure VIII-17). The design is sometimes

called the Russell collector after one of its

inventors. The troughs are oriented east to

west and a glass mirror is bonded to a concrete form. The focal line moves in a circular arc as the Sun changes position, and

the absorber pipe moves to follow it. The

pipe is a high-performance design and may

incorporate a secondary reflector to raise

the overall concentration ratio to 60:1.

General Atomic hopes that this design

can eventually be built to sell for less than

$65/ m

2 installed after a large production industry is established but, of course, this cost

has not been verified. The design is well
Ch. VIII Co//ectors ● 2 6 9

SOURCE Nontechnical Summary of D@trlbuted Collector Concepts ATR76(7523 -07)-1 (1) ERDA

Suited to casting in concrete. Sandia has

ordered a 7-ft-wide by 400-f t-long prototype

from General Atomic being tested in connection with its solar total energy system. 34

scientific-Atlanta. Scientific-Atlanta, Inc.,

is a General Atomic licensee and IS produc -

ing 2.44 x 3.05 m (8 by 10 ft) collectors

(figure VI 11-18). Rather than embedding mirrors in concrete, Scientific-Atlanta uses steel

sheet-metal ribs on which the low-iron, backsilvered glass mirrors are fixed. The collectors bolt end-to-end to reduce optical endIosses and interconnection pipe expense

The receiver is a high-performance, tubularevacuated collector manufactured by Corning Glass Works. Scientific-Atlanta installed

a 50 m2 prototype at the Georgia Institute of

Technology in 1975.

J4j Russel (General Atomic Co.], Private commun!catlon, March 1977

Figure Vlll-18.— Russell Collector by Scientific”Atlanta, Inc., Installed at Georgia Institute of Technology

PHOTO John Furber
270 ● So/ar Technology to Today’s Energy Needs

AAI.-AAI is also developing a fixed trough

with a tracking receiver. The trough has a

circular cross section and the concentration

ratio is 8:1. It is not designed to produce the

very high temperatures of the Genera l

Atomic design. The effective cost of the

system would be considerably less if the

trough could be used as a part of a building

roof. The axis is oriented east to west and a

wide range of trough sizes is possible. The

receiver is similar in construction to a long,

narrow, flat-plate collector mounted upside

down on long arms above the reflecting

trough. The refIecting surface is glass mirror.

Linear Heliostats/Stationary Receiver

The linear-segmented reflector concept

was originally suggested by Professor F.

Francia and tested in 1963 at the Universite

de Provence in Marseilles. ” The design has

attracted the interest of several U. S. manufacturers. The basic approach is illustrated

in figure VII 1-19. The receiver is fixed and

,

“Arrow & Francia, /ourna/ of Solar Energy, Vol 11, 1,

1967.

the light is focused on it by an array of long,

narrow mirrors which follow the Sun. The

design has several advantages: the receiver

pipe carrying heated liquids does not move;

the moving mirrors are all relatively small;

and al I mirrors are driven by a single tracker.

SunTech Systems (a subsidiary of Sheldahl) is producing a concentrator consisting

of 10 long, narrow reflectors which direct

the Sun onto a single stationary receiver

pipe. Each reflector is 6.1 x 0.30 m (20 by 1

ft) and is slightly curved to concentrate the

Sun by four times onto the absorber. This

gives an overaIl concentration ratio of 40X.

Two of these modules are placed end-toend and driven by a single tracker.

This unit can withstand very high winds,

and the slats are automatically turned u p -

side down when the Sun isn’t shining to prevent frost formation or snow accumulation.

Sheldahl received a $176,156 ERDA contract

in 1976 to develop the design. A prototype

has been installed at Sandia.

Itek is doing research on a similar linearsegmented reflector. However, Itek’s receivFigure Vlll-19.– ITEK Distributed Collector Concept With Inset Showing the

High” Performance Receiver Design

Pyrex tube enclosure

(6 inch diameter)

Insulation

- (rein-k) / Movable
Ch. Vlll Collectors ● 2 7 1

er is designed for hi gh performance at even

higher temperatures. AAl is also interested

in this concept and has buiIt a prototype.

TWO-AXIS TRACKING

Solar collectors capable of producing

temperatures above about 3000 C must be

able to track the Sun by rotating about two

independent axes. The most common systems are the equatorial and the azimuth

mount. The equatorial mount is advantageous because all tracking during the day

follows one axis (parallel to the Earth’s axis

of rotation). The change in the Sun’s elevation is only a maximum quarter-of-a-degree

per day and can be compensated for by a

simple adjustment of the declination axis

every few days. AlI other tracking systems

require active tracking along both axes during the day. The azimuth mount is often

used because of its mechanical simplicity;

this mount, for example, is used for most

radar dishes and for naval artillery. The

azimuth axis is vertical and the altitude or

elevation axis follows the Sun’s movement

from horizontal to vertical.

Two-dimensional concentrators fall into

three classes:

1.

2

3

Systems which focus light on a smallpoint receiver which moves with the optical system.

Heliostat systems, where a large field of

individual mirrors focus on a central

receiving tower

Stationary concentrators with tracking

receivers.

Collector and Receiver Both Tracking

Most early two-axis tracking systems used

a single large reflecting dish which looked

much Iike a radar antenna. These systems

may prove to be the most attractive in applications where there is an incentive to focus

large amounts of energy on a single point

(e g., where a small heat engine or sophisticated photovoltaic device is employed). In

many applications, however, it is possible to

use a number of smaller concentrating units

focus ing light on a series of relatively small

receivers. These smalI units typically are

ganged together into a single tracking unit.

Determining the optimum size of the individual concentrator device will require a

substantial amount of engineering analysis

for each application,

Ganged Concentrators.–Both mirrors and

Fresnel lenses can be used in a ganged concentrator. Mirrors have the advantage of

being less expensive per unit of aperture and

do not experience chromatic aberation if

used to produce high-concentration ratios.

(Mirrors will probably be preferred in systems with concentration ratios greater than

500 x ).3

’ 37 The Varian Corporation has built

a two-axis tracking device using an array of

7 rows of 17 parabolic mirrors each 25 cm

(10 in) square, mounted on a single tracking

platform (see figure VI 11-20). Each mirror

provides a concentration of 1,000 x .38

MIT and the National Patent Development Corporation are doing research on a

moduIar, mirror-concentrater/photovoltaic

system in which the separate, round, parabolic mirrors are connected to a common

tracking system (see figure VI 11-21). A small

secondary mirror in front of each of the

main mirrors reflects Iight back through a

hole in each main mirror onto a solar cell.

This reduces any shadows from the cell and

cooling water pipes. A concentration ratio

of 300-500:1 is felt to be optimum. The system is designed to produce both electricity

from the photovoltaic cells and therma l

energy from the liquids used to cool the

cells. The company hopes to be able to sell a

complete system of unspecified size for less

than $5,000— a system which wilI last at

least 10 years with minimal maintenance,

Fresnel lenses have the advantage of

being somewhat less sensitive to tracking er3’L W James (Varian), private communication ,

May 6,1976

“W R Lee (Swedlow, Inc ), private communi( ation, Nov 17, 1976

36L W James (Varian Associates, Baton Rouge, La ),

phone conversation, April 1976

3’Washington Post, June 5,1976, p Al
272 ● Solar Technology to Today’s Energy Needs

Figure VIII-20.—The Varian Two-Axis Concentrator Using GaAs Photovoltaic Devices

rors than mirror systems, and they can be

designed to provide a uniform intensity

across the receiver surface. The lenses can

be made from durable plastic materials and

it may be possible to manufacture them

very inexpensively in mass production facilities. The special designs required for solar

applications would not add to the cost of

manufacturing the systems. 40 4

‘

4 0W R Lee (Swedlow, Inc ), private communication, Nov 17, 1976.

*’L. W James, et al (Varlan), “Performance of a 1-

kW Terrestrial Array of AICaAs/GaAs Concentrator

Solar Cells, ” 12th IEEE Photovoltaic Specialists Conference, Baton Rouge, La , Nov 15-18, 1976

PHOTO Courtesy of The Varlan Corporation, 1977

The best material for Fresnels will probably prove to be some kind of acrylic plastic

even though this material is considerably

more expensive than glass. It is very difficult

to cast glass with the accuracy and sharpness that is possible with acrylic, which is

not as viscous as glass when it is cast, Acrylics can be made which can withstand outdoor climates for over 20 years.” 42 43 44 Swed -

4 2R P Falconer (Lectric Lltes Co , V Pres ), private

communication, Oct 15, 1976

“W R. Lee (Swedlow, I nc ), prlv,~te communication, Nov 30, 1976.

“L C Rainhart and W. P Schimmel, Jr (Sandia

Labs), “Effect of Outdoor Aging of Acrylic Sheet, ”

SAND 74-0241
Figure VIII-21 .—An MIT Design for a Small

Two-Axis Tracking Unit

low, Inc., has estimated the price at which

they could sell cast-acrylic Fresnel lenses at

various production levels. These estimates

appear in figure VI I I-22. Swedlow has invested about $200,000 in solar lens research

at this writing, and the firm estimates that a

large-scale production line could be operating in 22 months if a decision is made to

initiate manufacture. 45

Sandia Laboratories, Albuquerque, has

built a 1 kWe photovoltaic test bed using

pressed-acrylic Fresnel lenses supplied by

“it’ R ~.ee (Sw[’dlow, I nc ), private commu nlcatlon, Oct 14, 1976

Fresnel Optics,

collector consis

Ch. Vlll Collectors ● 2 7 3

Inc., of Rochester, N.Y. This

ts of a checkerboard o f

square Fresnel lenses mounted on the top

surface of a flat box (figure VI 11-23. )

A collector using Fresnel lenses in a

design similar to the MIT device discussed

previously has been designed for use on an

experimental basis by the RCA Corporation

(see figure VI 11-24). This kind of design has a

relatively low profile and can be integrated

into a house or building more easily than

any other type of two-axis tracking system.

Large Paraboloid. -Large tracking parabolic

dishes are commercially available but current commercial designs are much too expensive for any practical solar energy system application.

The Jet Propulsion Laboratory (JPL) of the

California Institute of Technology has developed a conceptual design for a high-efficiency, low-cost paraboloidal solar powerplant (figure VII I-25). The reflecting surface

is made of commercially available silvered

mirrors which are curved sIightly by glueing

them to concave pieces of foam glass. These

curved pieces are then mounted on a metal

framework and all are aimed at a single

focal point, The entire framework tracks the

Sun.

The tracking paraboloid system is wel l

suited for applications using a Stirling or

Brayton engine and electric generator. JPL

has estimated that it may be possible to

mass produce and instalI these collectors for

less than $120/m

2

.

46 The mirror and foam

glass surface cost about $20/m2

. This is admittedly optimistic since precision tracking

radar dishes now cost about $322/m 2

,

47 b u t

the solar devices could be produced i n

much greater quantities and would not need

to be as precisely constructed or as reliable,

46M K Selchuk, et a I , So/ar Stir/ing Power Generation. Systems A na/ys is and Preliminary Tests, Pro -

ceed ings of the 1977 Annua I Meeting of the American

SectIon of the International Solar Fnergy Soc(ety,

orlando, Fla , June 6-10, 1977, p 20-8

47 Selchuk, op cit., p 20-9
274 ● Solar Technology to Today’s Energy Needs

Figure Vlll-22.— Sales Price of Cast-Acrylic Fresnel Lens Versus Production Volume

Note:

SOURCE Urrsohclted Tecfmmal Proposal for Casf-Acry/lc Fresne/ Lenses for Scl/ar-Ce// Energy Generator?, Swedlow Report

No 873, September 30 1976 Swedlow Inc Garden Grove CA pp 5-3

The Carousel Collector. -Another approach

to two-axis tracking is illustrated in figure

VI 1 I-26. In this approach, a number of oneaxis tracking parabolic troughs are mounted

together in a platform which rotates to

follow the Sun. The system illustrated is

mounted on tracks, but it is also possible to

simply float the platform on a pond o f

water. ” A simpler one-axis tracking system

can be manufactured along the same lines

by rigidly mounting the trough concen -

trators on the rotating platform.

Heliostat/Central Receiver

The heliostat/central receiver arrangement can be scaled up to very large sizes,

although small systems may also be useful.

Such a system has an advantage over most

distributed collector field concepts in that

the energy is transmitted to the central

48 Solar Energy Digest (9)1 (1 977)

receiver as light rather than through an expensive piping network as heat.

Francia Solar Heliostat Tower.–Professor

Francia of the University of Genoa has had a

100 k Wt solar steam-generating statio n

operation near Genoa (S. IIario), Italy, since

1967 (figure VI 11-27). All of the mirrors in the

field are linked together and driven by a

single pendulum clock. A joint venture of

ANSALDO, S.A., a large Italian industrial

organization, and Messerschmidt of Germany is now selling solar steam-generating

systems of Francia’s design. The Georgia Institute of Technology in Atlanta bought a

400 k Wt test facility of this design from

ANSALDO. It began operating on th e

Georgia Tech campus in 1977. 49 In addition

to the innovative linked-mirror field, the

Francia design appears to have an unusually

4’S H Bomar (Georgia Institute of Technology),

private communication, Nov 13, 1976
Ch. VIII Collectors ● .275

—.——- 

Figure Vlll-23.— 1kWe Focusing Photovoltaic Test Bed at Sandia Laboratories, Albuquerque”

1 -square Foot Fresnel Lenses FOCUS on 2-in. -Diameter Solar Cells

PHOTO Courtesy of Sandla Laboratories
276 ● Solar Technology to Today’s Energy Needs

Figure Vlll-24.— RCA’S 300We Photovoltaic Concentrator

Figure VI II-25 .—JPL Paraboloid Design With

Stirling Engine at Collector FOCUS

SC)URCE Prepared by OTA usng manufacturer s iiatd

SOURCE Prepared by OTA using JPL Information

PHOTO Courtesy of RCA

high thermal efficiency, Professor Francia

has reported a net collection efficiency o f

73 percent. 50 Analysis at Georgia Tech indicates that even better results can be obtained by using molten salt or liquid metal

instead of steam in this type of receiver.51

Francia’s design has been used by Mitsubishi Heavy Industries, Ltd., of Hiroshima

to build the 7 kWt test facility (shown in

figure VI 11-28). Mitsubishi changed the heliostat design slightly. to allow the field to

move its focus from one receiver tower to

another. This improvement has been incor-

‘“G Francia, Large Sea/e Central Receiver Solar Test

Facilities, ProceecJ; ngs of the International Seminar on

Large Scale Solar Energy Test Facilities, Las Cruces, N

Mex , Nov 18-19, 1974, pp. 101-136, p 130

“R W. Larson (Professor, Ceorgla Institute of Technology), private communication, September 1976.
Ch. Vlll Collectors ● 277

Figure Vlll-26.— Sunpower Systems Solar Powerplant

—--7 .

.

\

.

SOURCE Sunpower Systems Corp Tempe, Arlz
278 ● Solar Technology to Today’s Energy Needs

Figure VIII-27.—Francia 100 kW+ Solar Powerplant

(Closeup

.

of heliostats showing trackingIinkage on back)

PHOTO Courtesy of Georgia Tech

porated into the test facility sold to Georgia

Tech by ANSALDO. 52

Federally Sponsored Heliostat/Central Receiver Designs. –DOE’s biggest solar investment in collector development thus far has

52G Beer and R Flores (ANSALDO S P A ), private

communications, Oct 28-29, 1976

been directed to the design of large heliostat/central-receiver electric powerplant s

designed primarily for desert regions. A

number of variations on the basic design

have been funded by DOE and the Electric

Power Research Institute. Present plans call

for a 100 MWe pilot plant, preceded by a 5

MWe test facility at Sandia Albuquerque

and a 10MWe demonstration plant at Barstow, Cal if. (table VI 11-3).

Three companies designed complete systems, and Boeing contracted to design just

the heliostats. The heliostats designed all

have refIector areas of approximately 40 m2

,

but design s differ considerably (figure

VI 11-29). Boeing’s design employs a thin

layer of Kaptan stretched over a lightweight

frame. The system is shielded from the

weather with a transparent plastic bubble,

The Honeywell design uses six 2.1 x 3.1 m

(7 by 10 ft) mirrors mounted on a common

turntable. The mirror mounts are aluminum

“egg crate” with plastic filling, The Martin

Marietta/Georgia Tech design uses 25, 1.22

by 1.22 m (4 by 4 ft) mirrors mounted on a

common tracker. This array forms a crude

parabola with a concentration ratio of approximately 5.3:1. The McDonnell Douglas/

University of Houston design uses a single

37 m’ (400 ft2

) mirror mounted on large-cell

honeycomb material.

53

The three receiver concepts also differ

considerably. Martin Marietta is designing a

high-efficiency cavity receiver to face a

heliostat field to the north. The Honeywell

receiver accepts Iight through an opening in

its bottom, and the receiver tower is located

n the center of the heliostat field. McDonnell-Douglas is designing an open panel receiver to be located slightly south of the

center of the heliostat field (figure VI 11-30).

The Department of Energy has selected

the McDonnell-Douglas design for its initial

10 MW demonstration. An artist’s concept

of the completed 10 MW facility is shown in

—

“Data on these collectors was taken from Survey of

Several Central Receiver Solar Therma/ Powerp/ant

Design Concepts, J PL, August 1975.
Ch. VIII Collectors ● 2 7 9

.

Figure Vlll-28.— Mitsubishi (7 kWt

) Heliostat/Receiver Test Bed

Specifications

Energy Collected about 7 k Wt

Mirror 0,3 x 0.4 m2

, 120 pieces

Heliostat 60 pieces

Tower Height 3m

Absorber Cavity type 0.5 x O 6 m2

Heat Carrier Air. max 800° C

SOURCE K Yanagl (Mroshlma Technical Institute Mltsublsht Heavy

Industries Ltd ) Solar Energy Collecting Test Apparatus
280 ● Solar Technology to Today’s Energy Needs

Table Vlll-3.—Characteristics of Competing Designs for the 10 MWe Solar Central Receiver Powerplant

Boeing Honeywell Mart in-Marietta

Annual energy output

(MWh)

Collector Subsystem

Heliostat construction metalized plastic

reflector, aluminum

and steel frame

Number of heliostats 3,146

Reflective surface per 29 m2

heliostat

Total area reflective 91,234 m2

surface

Field size

Receiver subsystem

Receiver type

Tower height

Receiver working fluid

Storage subsystem

Storage mechanism

Storage media

Electrical generation

subsystem

Turbine rating

Turbine fluid

4.3 x 104

glass mirror, lowprofile steel frame,

multifaceted, focused

2,320

40 m2

92,800 m2

308 m radius

vertical cavity

146 m

water/steam

latent heat

salts

15 MW

steam

3.4 x 104

glass mirror, steel

frame, multifaceted,

focused

1,718

37.2 m2

63,866 m2

565 m x 565 m

horizontal cavity

137 m

water/steam

sensible heat

HITEC/hydrocarbon heat

transfer fluid

12.5 MW

steam

McDonnell-Douglas

3.6 X 1 0

4

glass mirror, steel

frame, multifaceted,

focused

2,350

30.8 m2

72,380 m2

527 m x 527 m

external absorber

101.4 m

water/ steam

sensible heat

rocks/ hydrocarbon heat

transfer fIuid

15 MW

steam

SOURCE Department of Energy

figure VllI-31, and construction of McDond

nell-Douglas heliostats or a 5-MW system is

shown in figure VIIl-32

Stationary Concentrator ‘ g Receiver

This concept uses a fixed-mirror/movingreceiver system with two dimensions of concentration. A section of a sphere made from

mirror surfaces produces a radial Iine-focus

pointing at the Sun (figure VI 11-33). Only the

receiver pipe moves to follow this line of

high-intensity sunlight around the inside of

the stationary dish. Because the dish does

not track, this system collects much less

light in the early mornings and late afternoons than tracking dishes. Its success will

depend on whether initial and operating

costs will be sufficiently below the costs of

tracking dishes to compensate for its disadvantages.

At least three organizations are currently

working on this concept— Environmental

Consulting Services, Inc., of Colorado, ESystems Garland Division in Texas, and

C.N.R.S. (the French national petroleum

company). E-Systems is a large, high-technology company which has built and installed dozens of fully tracking parabolic

communications dishes and also refinished

the huge, stationary spherical radiotelescope reflector at Arecibo, Puerto Rico. As a

result of the firm’s experience with both

types of collectors, it considers the fixedsphere design a more economical solar collector even when the reduced performance

is taken into account. SmalIer colIectors can

be integrated into a building’s roof, and

larger dishes could be mounted in an excavation to serve several buildings, a factory, or a community.
Ch. Vlll Collectors ● 2 8 1

Figure Vlll-29.– Pilot Plant Heliostat Concepts

Boeing

Martin Marietta

McDonnell Douglas

SOURCE Prepared by OTA using manufacturer’s data
282 ● Solar Technology to Today’s Energy Needs

Honeywell

Figure Vlll-30.— Pilot Plant Receiver Concepts

McDonnell Douglas

SOURCE Prepared by OTA using manufacturers data

Figure VIII-31 .—McDonnell Douglas 10-MW Pilot Plant Design. The Heliostat Field Surrounds the Thermal Storage

(Circular Tank), Tower, and Electrical Generation Subsystems. Note the Octagonal Shaped Heliostats
Ch. VIII Co//ectors ● 2 8 3

Figure VIII-32. —The 5-MW Central Receiver Demonstration Under Construction in Albuquerque, N. Mex.

L

‘.e

ii

‘

Photograph by John Furber

Figure VIII-33. —Cross-Section of Stationary Hemisphere Concentrator

Heat

transfer . A

Fixed

absorber

Turbine

r

SOURCE E. Systems Inc absorber facility
284 ● Solar Technology to Today’s Energy Needs

ENVIRONMENTAL IMPACT S

The two largest environmental effects of

the manufacture of solar collectors result

from the emissions associated with th e

energy generated to manufacture the devices, and the impact of the collectors on

land use in cases where the collectors cannot be integrated into the roof, walls, or immediate landscape of a building. These

problems are discussed in some detail in

chapter VI 1. There will also be a number of

occupational health and safety issues associated with the manufacture of specific collector designs,

WORKING FLUIDS

Some of the chemicals used in sola r

domestic water heaters to slow corrosion in

the collector and to prevent the working

fluid from freezing can be harmful if the collector fluid leaks through a heat exchanger

and mixes with the hot-water supply. I n most

regions, double-walI heat exchangers are required by local codes to protect against accidental leakage when potentially harmful

chemicals are used. A lethal dose of ethylene glycol which is commonly used as an

antifreeze in colIector fIuids is about 100 gm

(1.3 lb) for an average adult. About 1/2 liter

(18 O Z) of the glycol-water mixture used i n

typical systems would have to be ingested to

obtain a lethal dose. It is unlikely, however,

that the heat exchangers wouId leak so massively that undiluted collector fluid would

appear in the hot tapwater without being

detected. Chronic ingestion of smal l

amounts of ethelyene glycol can, however,

cause “moderately toxic systemic effects.” 54

Some of the working fluids proposed for

use with higher temperature systems can

also be caustic or toxic if leaks develop in

the plumbing systems, but these chemicals

would not come into close proximity t o

potable water.

“J. G. Holmes, “Environmental and Safety implications of Solar Technologies, ” ISES 1977 meeting, p,

285

Glycol and other heat transport fluids

degrade, and must be replaced periodically.

This disposal could also create environmental problems. 55

MANUFACTURING HAZARDS

Many of the plastics being used or proposed for use in inexpensive solar collectors

can create hazards for employees in plants

manufacturing the materials, even though

most of the plastics are not harmful after

they are fabricated and units installed .

Plastics are used in collector covers, Fresnel

lenses, thin mirror surfaces, piping, and a

variety of other places in solar systems.

Most of these materials are manufactured in

substantial volume today and the solar industry would only have the effect of increasing the number of persons exposed to any

risks that may now exist. None of th e

materials described below are uniquely required for the manufacture of solar collectors. If it is determined that any of the

materials now in use create unacceptable

environmental hazards, substitutes could

undoubtedly be found.

In simple flat-plate collectors, thin strips

of Styrofoam or similar materials are often

used as insulation or backing; these compounds contain styrine, which the EPA classifies as a suspected carcinogen. Some silicone elastomers and polysulfide-based compounds are used as sealants in solar collector units; silanes, contained in the silicone

elastomers, are considered moderately to

highly toxic during the manufacturing process. Organic sulfides, compounds found in

polysulfide-based materials, can cause an

acute reaction that could cause a person to

become unconscious after one alcoholic

drink.

Urethanes are contained in polyurethane

foams, which are often used as insulation in

55J G. Holmes, op. cit
Ch. V/// Co//ectors ● 285

plumbing connected to solar collectors. EPA

suspects that urethane is a carcinogen.

The transparent covers used on flat-plate

collectors are often made of acrylic plastics

or plastic films such as Mylar, Tedlar, Kynar,

Korad, and Teflon. Some plastics contain

methyl methacrylate, which is considered to

be moderately toxic by the EPA. Others contain fluorocarbons which are only slightly

toxic, but can be an environmental problem.

(See the discussion of fluorocarbons i n

chapter VI 1.)

Concentrating lenses and reflecting mirrors are generalIy acrylic-based plastics,

which are considered moderately toxic. And

coatings or encapsulant on flat-plate solar

cells may be made from plastic-based films,

which contain melamine, a moderately toxic

material.

Vinyl chlorides are used extensively in the

manufacture of a number of inexpensive

collectors. Unfortunately, vinyl chlorides

(along with other plastics) cause disposal

problems and can be hazardous. The materials are not biodegradable, and they may

produce toxic fumes if burning is used as a

means of disposal. Research is underway to

develop biodegradable plastics to help alleviate the plastic disposal problem.

COLLECTOR COST S

FOB COLLECTOR PRICES

Unless otherwise noted, the collecto r

prices cited in this chapter (including those

shown in tables VII I-4 through VI 11-8) are

FOB factory prices and do not include shipping or installation. Estimates of collector

instalIation costs vary greatly (see discussion in volume 11, chapter IV). Table VII I-9

contains an estimate of installation costs

which may be obtainable in a mature

market.

In a few cases involving larger systems,

the companies indicated that they would install only the entire system and would not

sell collectors separately, Where a price

range is given, the lower price corresponds

to a large order while the higher price corresponds to a smalI order. As noted, some

manufacturers of flat-plate collectors, and

the foreign distributors, will sell directly to

individuals at these prices, Most, however,

sell only to distributors, contractors, and architect/engineering firms,

All pricing data in this section are in 1976

dollars. Prices include headers, but exclude

the controls, pumps, and interconnecting

pipe which most collectors require. Prices of

tracking collectors include trackers, bearings, drive motors, and tracking controls,

but exclude the cost of pumps, storage, and

controls. Prices for collectors other than flat

plates are in dollars per-square-meter of

useful aperture, while flat-plate collector

prices are per-square-meter of gross collector area. This gross area includes the area

blocked out by the “window frame” an d

thus makes the flat plates appear a bit less

costly than if they were priced on a useful

aperture basis.

Each manufacturer was contacted directly and asked for quantity factory prices to

contractors, excluding shipping, installation,

and interconnecting piping. Since most collectors other than flat plate are not yet in

mass production, manufacturers were asked

for both present limited-production prices

and what prices they projected in mass production. All prices were requested in constant 1976 dolIars and all inquiries were

made in 1976,

COLLECTOR SUMMARY TABLES

The following abbreviations are utilized

in tables VII I-4 through VII I-8:

Sel. Surf. –Selective surface absorber ab-
286 . Solar Technology to Today’s Energy Needs

Table Vlll-4.—Stationary Flat-Plate Collectors

Present wholesale Expected price

price f.o.b. factory when in Design

Company Type/feature ($/m2

) mass product ion Status temperature

Thomason flat plate

trickle system

1 glass cover

Sun works flat plate

sel. surf.

1 cover, glass

PPG flat plate

(opt. sel. surf. )

2 glass covers

Al roll-bond

(opt. Cu roll-bond)

flat plate

(opt. sel. surf. )

2 Tedlar covers

Mark II

Al or Cu roll-bond

covered with

evac. tubes

heat mirror

Unitspan Cu tube and sheet

Reynolds

Alum inure

N. V. Philips

2 glass covers

Honeywell/ flat plate

Lennox Cu tube, steel

sheet, 2 etched

AR glass covers

set. surf.

Calmac Flexible mat o

Manufacturing black EPDM

Corp. tubes, 2 fiberglass covers.

32-43 commercial 67° C

to consumer

85-114 about same commercial 57 0

-97“c

product ion

80-107 same commercial mass 57°-97 “c

product ion

54-65

—

86-92

to consumer

145 or less

same

$118

commercial

R&D

about same commercial

less commercial

35-44 about

(Retail price;

some on-site

fabrication

required)

57°-97 “c

57 °-167°C

57 °-97° C

57 °-97°C

same commercial 57°-820°C

mass production

SOURCE Prepared by OTA using manufacturer’s data

Table Vlll-5.— Foreign Stationary Collectors on U.S. Market

Present wholesale price

Foreign f.o.b. U.S. Design

company Country U.S. Distr. Type distr. ($/m2

) temperature

Miromit . . . . . . Israel American

Heliothermal

Corp.

SAV . . . . . . . . . New Zealand Fred Rice

Product ions,

Inc.

Amcor . . . . . . . Israel Sol-Therm

Corp.

flat plate 119-180 57 °-97°C

1 glass cover

sel. surf.

steel tube

sheet

cylindrical 500 57°-97°C

colIector

incorporates

storage

flat plate 119-147 57°-970°C

1 glass cover

steel tube &

sheet

SOURCE Prepared by OTA using manufacturer’s data
Ch. Vlli Collectors ● 2 8 7

Table VIII-6 . —Stationary Tubular and CPC Collectors

Geometric Present wholesale Expected price

concentration price f.o.b. when in

Company Type/feature ratio factory ($/m2

) mass production Status

Owens-l llinois

KTA

Philips

General Electric

Steelcraft, Inc.

M-7 International

evac. glass tubes

sel. surf. on glass

inner tube. White

refIector

Cu absorber in

glass tube. Half

siIvered

Mark I evac. glass

tubes half silvered;

heat mirror coating

evac. glass tubes

sel. surf.

stationary external

mirror

alzak mirror CPC

evac. glass tube/

sel. surf. receiver

glass cover

solid plastic CPC

for solar cells

— $215 (array aperture excl. headers

and end caps)

— 85-104

— —

— —

— 269

(end of 1976)

(excluding rack)

5 —

107-130

58-80

129

48-81

161-215

(end of 1977)

(excluding rack)

only slightly

more expensive

than conventional solar

cell packaging

pilot prod.

demon. &

testing

commercial

product ion

R&D

pilot

product ion

commercial

production

(end of

1976)

have prototype; need

capital for

tooling

Design

temp.

97 °-147° C

57 °-97°C

57°-167°C

57 °-167°C

204° C

electricity

SOURCE Prepared by OTA using manufacturer’s data

sorbs light well but does not rad i

heat as well.

Flat Plate— Flat-plate solar collector.

ate

Heat Mirror— Selective heat mirror coating

on transparent cover allows sunlight

to enter but reflects back infrared

heat trying to escape.

Opt. —Optional; available at extra cost.

Al — Aluminum.

Cu —Copper.

CPC– Compound parabolic cross-section

concentrating solar colIect

Evac. – evacuated.

AR – AntirefIection coated.

COLLECTOR PERFORMANC E

The only accurate test of the value of a

collector is the amount of useful output

which it can provide per dollar of Iife-cycle

investment, Unfortunately, there is no simple way to determine this useful output

since the useful work done by a colIector

depends on the load, the quantity and quality of sunlight which is available, the size

or.

and type of storage devices used, local temperatures and wind velocities, and correlations between energy demands, weather,

and available sunlight: a system whic h

operates effectively in a home-heatin g

system in Albuquerque may be extremely inefficient connected to an air-conditioner in

Boston.
288 Ž Solar Technology to Today’s Energy Needs

Table VIII-7. —One-Axis Tracking Collectors

Present wholesale

Geometric price f.o.b. Expected price

concentrate ion factory ($/m2

)

Company

when in Design

Type/feature ratio (incl. tracker) mass production Status temperature

AlbuquerqueWestern Inc.

Beam

Engineering

Sandia Labs

AAI

General Atomic

co.

Northrup, Inc.

Suntech

Systems, Inc.

Itek

Acurex Corp.

(6’ wide)

Acurex Corp

(4’ wide)

Solartec Corp.

Scientific

Atlanta

parabolic trough 20

tedlar window

Cu pipe

parabolic trough

parabolic trough

evac. glass tube/

sel. surf. abs.

fixed trough; ~ 8

tracking receiver

fixed stepped 60

trough; tracking

receiver

linear Fresnel ~ 10

lens; sel. surf.

on Cu absorber

linear heliostat 40

linear heliostat

linear cavity

receiver

parabolic trough 58

anodized Al mirror

glass tube

sel. surf. absorber

(see above)

parabolic trough

anodized Al mirror

(see Gen. Atomic)

evac. glass tube/

48-51 (incl.

250 tracker to

drive 20-28

troughs)

235 or less

(see Acurex)

—

—

133-180

215-270

—

160-240

140-210

100-172

145-161

(developing advanced design)

“much less”

80% learning

curve to very

low price

54-65 w/roof

cred. or 86-97

retrofit

(installed)

(advance

design)

46-108

102

less

86

about same

about same

commercial

product ion

commercial

product ion

demonstrate ion

R&D

R&D

commercial

product ion

prototype

testing

R&D

commercial

product ion

commercial

product ion

commercial

product ion

commercial

product ion

32°-1OO°C

93° C

317°c

117°c

497° C

93° C

177°-317°C

537° C

60°-31 1‘C

600-1 77“C

204° C

204°-326°C

set. surf. absorber

glass mirror

SOURCE Prepared by OTA using manufacturer’s data

It is only possible to evaluate a collector

accurately by examining its performance as

a part of an integrated system operating to

serve a particular building in a specific geographic area. For this reason, primary attention in this report has been directed to evaluating the performance of integrate d

systems.

Evaluating the performance of integrated

systems requires a technique for computing

the amount of output which can be expected from a collector under different conditions. The calculations used to perform

this analysis are explained in some detail in

the appendix to this chapter. The basic approaches to the analysis of collector per-
Ch. VIII Co//ectors ● 289

Table Vlll-8.—Two-Axis Tracking Collectors

Present wholesale

Geometric price f.o.b. Expected price

concentration factory ($/m2

) when in Design

Company Type/feature ratio (incl. tracker) mass production Status temperature

ANSALDO/

Messerschmidt

E-Systems, Inc.

Sandia Labs

JPL

Varian

DOE

contractors

ANSALDO/

Messerschmidt

National

Patent

Development

ANSALDO/

Messerschmidt

Sun power

System Corp.

ganged kinematic

heliostat /tower

fixed dish

tracking receiver

multiple Fresnel

lens w/solar celIs

acrylic lens

parabolic dish

9.75 m square

glass mirror

multiple parabolic

dishes w/solar

cel Is

central power

station, heliostat/tower

parabolic dish

832 m2

100 kWe

ganged glass

parabolic dishes

w/solar celI

Heliostat /tower

5MWth/1MWe

parabolic/trough

carousel

250-500

50-100

1000

1000

300-500

96

?

—

224*

(w/o cells)

—

650-1 ,000’

(w/o cells)

437-492/m2

installed

govt. demo)

1,800

—

385

(incl. tower&

boiler)

175

50-53/m2

installed

(w/o cells)

115

very low

70/m2

heliostats

14/m2

tower

receiver

less

7

less

about same

ready for

order

R&D

prototype

R&D

R&D

ready for

order

R&D

ready for

order

commercial

600° C

260° C

27°-100°C &

electricity

815° C

27°-1OO°C &

electricity

477° c

550” C

27°-100°C &

electricity

600” C

500-2600C

product ion

“ Estimated based on laboratory prototype excludlng des!gn and toollng costs

SOURCE Prepared by OTA using manufacturer’s data

formance will be explained briefly in the

following section and some general conclusions will be drawn about the advantages

and disadvantages of the major categories

of colIector designs.

The next two sections examine the effects

which are most important in determining

collector performance and a final section of

this chapter compares the performance of

five generic types of collectors operating in

the four cities examined in this study.

THE ENERGY AVAILABLE

FOR COLLECTION

The amount of light energy which ultimately reaches the receiver of a collector

depends on two things:

1. The quantity and quality of the sunlight

which reaches the Earth’s surface, and

2. The tracking geometry of the collectors,
290 • Solar Technology to Today’s Energy Needs

. .

. .

. .

. .

. .

.,

. .

. .

“ n

“ u

I l l I I I

I

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. .

. .

. .

. .

.,

. .

. .

. .

. .

. .

. .

. .

. .

. .

. .

. .

. .

. .

. .

c. . . .

.- . . . .

(n . . . .

LL
Ch. VIII Collectors . 291

The Solar Resource

The amount of light which can be collected by a solar device on the Earth’s surface is limited by the cycle of day and night,

clouds, atmospheric turbidity, seasonal

changes which result from the tilt of the

Earth’s axis of rotation (the axis tilts toward

the Sun during the summer in the northern

hemisphere and the elliptical shape of the

Earth’s orbit brings the Earth closer to the

Sun during the winter) and atmospheric dust

which may result from volcanic eruptions or

local air pollution. It is also possible that

there are long-term cycles in the amount of

energy generated by the Sun itself, and there

has been speculation that such cycles are

responsible for cyclic ice ages and periods

of severe cold which fall short of ice ages

(such as the cold period which grippe d

Europe during the reign of Louis XIV].

There is very little information available

about long-term changes in the amount of

energy produced by the Sun or about longterm cycles in the net clearness of the

Earth’s atmosphere. It has been possible,

however, to assemble continuous measurements of the intensity of energy reaching the

Earth on a clear day from 1884 to the plesent by combining records taken at several

U.S. sites. The result is shown in figure

VIII-34. It can be seen that changes of 10

percent are typical, but that larger changes

can result from major volcanic eruptions

even though these explosions took place

many thousands of miles from the sit e

where the sunlight measurements wer e

made. Following the explosion of Krakatoa,

for example, the sunlight reaching the Earth

fell by nearly 20 percent.

The variation in sunlight available for collection in different parts of the United

States is illustrated in figures VI 11-35 and 36.

These figures show the solar resource in two

ways:

1. The total amount of sunlight falling on

a horizontal surface (which includes

both the energy received directly from

the sun and the “diffuse energy” received by reflection from clouds and

2.

other particles suspended in the air),

and

The “direct normal” radiation–th e

energy received by a collector which

tracked the Sun’s motion precisely ,

keeping the Sun perpendicular, or “norreal, ” to the surface of the receiver.

 Tracking systems which focus sunlight on

a receiver can only make use of “direct normal” radiation. It can be seen that the basic

solar resource varies by about 25 percent

around the national average in June (which

is the sunniest month in most climates) and

by about 50 percent in December (which is

typically the least sunny month). The pattern of distribution of direct normal radiation is somewhat unexpected since there

seems to be more variation from east to

west than from north to south. Thus, there is

greater similarity between the amount of

direct normal sunlight available in Fort

Worth, Tex., and Columbus, Ohio, tha n

there is between Fort Worth and western

parts of Texas.

Several warnings are necessary before

proceeding more deeply into an analysis of

the availability of sunlight around the country. The data on which such analysis now

must be based is of poor quality in most

parts of the country; continuous records of

direct normal radiation are almost nonexistent. (One of the primary criteria in selecting

the cities used in this analysis was the availability of sunlight data. ) Stations which

measure direct radiation are located in three

of the cities chosen (Albuquerque, N. Mex.;

Blue Hill, Mass. —a town close to Boston;

and Omaha, Nebr. ). Even in these cities,

however, complete records are difficult to

obtain. Most information about direct normal radiation must be obtained indirectly by

applyi ng statistical ‘techniques to measurements of the total amount of radiat;on

reaching a horizontal surface. (These techniques are discussed in the appendix. )

Another limitation of the analysis is that it

used data taken in a single year— 1962 (1 963

for Boston). Better comparisons could be

made if results were averaged over a number of years to eliminate unusual effects
292 ● Solar Technology to Today’s Energy Needs

Figure VIII-34. —Variation of Direct Normal Component of Solar Radiation With Time

Northern hemisphere values: typical of air mass = 1.5 100% corresponds to approximately 0.94 kW/m2

.

The names on the graph refer to major volcanic eruptions.
Figure Vlll-35.— Mean Daily Total-Horizontal Solar Radiation (kWh/m2

)
294 ● Solar Technology to Today’s Energy Needs

Figure VllI-36.– Mean Daily Direct-Normal Solar Radiation (kWh/m2

)

6.0
Ch. VIII Collectors ● 2 9 5

which may be due to weather patterns in

any single year. A comparison between 1962

data and long-term averages given in the appendix indicates that, for example, in

Omaha direct normal sunlight was about 13

percent below normal in 1962 while i n

Boston it was about 15 percent above average (see table VII l-A-2).

.

One of the limitations of the maps shown

in figure VI 11-35 is that they seriously understate the radiation which is available for a

flat-plate collector installed in a northern

latitude. An optimum collector is not horizontal but tilted at an angle close to the

latitude angle, In northern climates, this optimum angle is quite far from the horizontal

plane in which the sunlight measurements

were made.

COLLECTOR TRACKING GEOMETRY

A comparison of the sunlight available for

tracking and nontracking collector s is

shown in figures VI 11-37 and 38 for the four

cities examined in detaiI in this study. Figure

VI 11-37 compares the energy available for

colIection by a perfect flat-plate collector

(e.g., one with no thermal or optical losses)

tilted at the local latitude angle with the

energy available for a perfect, fully tracking

collector (e. g., a fully tracking parabolic

dish). The annual output of these collectors

is summarized in table VII J-1 O.

Albuquerque is the only city examined

where the energy avaiIable for a fully tracking collector exceeds the energy collectable

by a perfect flat-plate device. (It will be seen

later, however, that when an analysis is done

which includes the performance of real collectors, the ordering is usually reversed.) The

difference between the solar resource available for the two types of colIectors is, however, so small in the cities studied that it is

perilous to make any kind of conclusive

statement, particularly given the poor quality of the data on which these comparisons

are based.

Figure VI 11-38 compares the solar resources avaiIable to a nontracking fIat-plate

and a fully tracking collector system with

two other collector geometries: the heliostat

system (in which an array of mirrors directs

light to a central tower), and a one-axis

tracking trough which rotates around a

polar axis (an axis which points at the north

star).

The heliostat system gathers less energy

than other tracking devices because: 1) the

heliostats are not turned to face the Sun

directly (these devices must point in a direction between the Sun’s direction and the

direction of the receiver tower), and 2) because in the computation used to prepare

the data shown, the heliostat devices were

packed in a way that allowed some heliostats to be shaded during part of the day.

This shading was somewhat greater than the

shading which occurred with a comparable

ground coverage ratio in a field of fully

tracking dishes; it is necessary for a heliostat

to have an unobstructed view of both the

Sun and the receiving tower. This small disadvantage of heliostat systems may be compensated in cost savings when integrated

systems are evaIuated.

COLLECTOR LOSSES

Up to this point, the analysis has shown

only the amount of energy which could be

provided by perfect collectors with different

tracking geometries. The energy provided by

real collectors falls below this theoretical

value because of imperfections in the optical systems, and because some of the collected energy is lost to the environment

without doing usefuI work.

Optical Losses

Four types of losses decrease the optical

efficiency of f tat-plate systems:

1. Reflection from glass or plastic covers

is typicalIy 8 percent for each cover

used and is greater when the sunlight

strikes the collector at an angle. Some

thin-plastic films have lower reflective

losses than glass. These losses can be

reduced if antireflective coatings are

used, but this adds to the collector cost.
296 ● Solar Technology to Today’s Energy Needs

—. . . . . . -— - . . —. . -. . - . . . — . . . . . . . . . Figure Vlll-37.— Perfect Flat-Plate Collector Tilted at Latitude

Angle and a Perfect Fully Tracking Collector

4

140

120

200

180

Boston

200

180

1

160

140

120

60

20

0

200

● ’

180

160

140

60

20

0

Omaha

OTA
Ch. VIII Collectors ● 2 9 7

Figure VIII-38.—Comparison of the Maximum Energy

Collectable by Four Types of Collectors Located

in Albuquerque (1962 Radiation Data)

28-842 () -2 0
298 ● Solar Technology to Today’s Energy Needs

2.

3.

4.

Table VllI-10.—Useful Radiation Incident on Flat-Plate

and Fully Tracking Concentrating Collectors,

Four Cities, in kWh/m2

/year

Collector type Albuquerque Boston Ft. Worth Omaha

Perfect flat plate (tilted

at local latitude) 2,217 1,481 1,742 1,665

Perfect fully tracking

collector 2,500 1,373 1,543 1,458

Ratio (tracking/fIat plate) 1.13 .93 .89 .88

SOURCE. OTA

Reflections from the absorber surface

are typically 2 to 10 percent, depending

on the type of absorbing surface used.

About 2 to 4 percent of the energy received is absorbed and heats each

cover glass used.

Dirt on the collector surface reflects

additional light if the collector has not

been cleaned.

The energy actually available to heat liquids

in a single cover flat-plate colIector, therefore, is on the order of 80 to 90 percent of

the energy incident on the device. Losses

will be greater during the morning and evening when the Sun strikes the collectors at

glancing angles and reflective losses are

greater.

In tracking systems, losses can result from

imperfect reflecting surfaces, reflections

from lenses, energy absorption in lenses, inaccurate pointing of the focusing system,

and inaccurate placement of the receiver. It

is possible to produce mirrors which reflect

over 90 percent of the Iight striking them but

concentrating systems now on the market

typically use light, inexpensive aluminum

reflectors which typicalIy only reflect about

70 to 75 percent of the light striking them.

Dirt and dust pose a greater problem for

concentrating systems than for the fIat-plate

devices since a significant amount of the

energy in light which strikes dirt on the

cover of a flat-plate collector eventually

reaches the absorber surfaces and is absorbed. Light deflected by dirt on a focusing

system, however, is lost completely. Data on

the effect of dirt accumulation on performance is very preliminary at present, and may

be critical in determining the net cost and

performance of tracking devices.

Thermal Losses

when the absorber of a solar collector is

heated, it loses energy back to the environment in three ways: direct radiation (mostly

as infrared radiation) as it is lost from any

hot body ; conduction; and convectio n

through the transparent covers. These losses

are proportional to the absorber surface

area and increase with the temperature of

collection. Concentratin g systems hav e

much less absorber area per unit of collector area (it is reduced by the magnification

of the concentrating optics) and typically

operate at much higher temperatures. I n

most cases, however, the reduced absorber

area more than compensates for the increased temperature. Concentrating systems

usualIy lose a smaller fraction of the energy

reaching them to thermal effects than flatplate collectors.

The Significance of the Loss Factors

The contribution of thermal and optical

losses to the net efficiency of several collector designs is illustrated in figure VIII-39. It

can be seen that optical losses dominate

collector performance in all cases. The effect of optical losses in flat-plate systems is,

in fact, understated since the losses calculated assume that the Sun is directly over
Ch. VIII Collectors ● 2 9 9

Table VIII-11.– Collector Characteristics Assumed in Preparing Figure VIII-39

1-ax is tracking

parabolic

Commercial trough with

Flat-plate 1 -axis improved Fully

Single collector tracking refIecting tracking

cover (tubular parabolic surface and parabolic

pond design) trough receiver dish Heliostat

.

Concentration ratio 1 1 60 60 1,000

Outlet temperature (0 F) (1) 90 200 300 600 1,500

Optical efficiency (including

pointing inaccuracies, dirt,

etc. ) (2) 0.75 0.68 0.53 0.65 0.81

Thermal loss coefficient (including

convection, conduction and radiatlon) in kW/m2

°C (referenced to

collector area) (3) 7.3 x 10– 3

2.0 X10-3 4.1 X1 O-4 1 .5X10-4 6.2x10

-5

500

950

0.83

6.4x1 0-5

NOTES (1) In all cases the Inlet temperature was assumed to be IOO° F less than the outlet temperature

(2) In all track{ng collectors, opt(cal efficiency Includes a 1OO. loss due to dirt

(3 I In computfng thermal losses. It was assumed that the am b!ent temperature was 60” F

SOURCE OTA

Figure Vlll-39.— Energy Balance for Five Collector Designs

(See table VIII- I 1 for Assumed Characteristics of Collectors)

A

B

Flat Plate Commercial

Parabolic

Trough

A— Half of Maximum Sunlight

(.5 kW/m2 Incident on Collector)

Improved

Parabolic

Trough

B

Full y Tracking Heliostat

Dish

B — 1/4 of Maximum Sunlight

(.25 kW/m2 Incident on Collector)

SOURCE OTA
300 ● Solar Technology to Today’s Energy Needs

the collector. The thermal losses shown in

the figure are somewhat below averag e

since in most climates solar intensity seldom

is above the maximum possible solar intensity, which is typically close to 1 kW/m2

. The

relative significance of thermal losses increases sharply as solar intensity de -

creases — e.g., during periods of partia l

cloudiness. Moreover, the ambient temperature chosen for comparison was 600 F to

show the average performance of collectors

throughout the year. During the winte r

months, the outside temperature will be

lower and the thermal losses proportionately higher. The thermal losses of the high

temperature collectors are, however, somewhat overstated since the inlet temperature

assumed is only 1000 F lower than the outlet

temperature. It is clear, however, that thermal losses are a relatively small fraction of

the energy balance of high-temperature systems.

THE NET PERFORMANCE

OF COLLECTORS

The results of an analysis which includes

both a calculation of the sunlight available

for a collector and the ability of a collector

to utilize the sunlight available is summarized in tables VII 1-12 and 13. This information was computed using data on sunlight

and ambient temperatures available fo r

each city for each hour of the year 1962.

Several observations can be made on the

basis of these figures:

1. If systems are ranked in each city by the

2

total annual thermal output produced,

the ranking is, with a few exceptions,

the same in each city.

The only concentrating system which

produced less annual thermal output

than the flat-plate system was the commercial parabolic trough system.

3.

4.

5.

The fully tracking dish produced the

largest output in all cities, giving nearly

25 percent more than the best singleaxis devices and nearly 60 percen t

more than the f tat-plate systems.

Measured in terms of useful collector

output, Albuquerque has almost twice

the solar resources as any of the other

cities examined. The performance of

collectors in Boston, Fort Worth, and

Omaha was strikingly similar.

The pond collectors typically have very

low performance during the winter, particularly if high outlet temperatures are

desired.

The results of this analysis indicate that

concentrating systems can provide much

more useful thermal output than simple flatplate devices of the same area.

Even parabolic trough devices whic h

make use of known techniques for improving output were superior to the flat plate in

each city. This consistent inferiority of the

flat-plate system occurred in spite of the

fact that the flat-plate device chosen for

analysis was a relatively sophisticated and

efficient system. This seems to indicate that

optical advantages of flat-plate systems

(chiefly their ability to gather diffuse sunlight) is more than offset by the advantages

offered by concentrating systems (e. g.,

tracking and reduced thermal losses). A

valid comparison of systems can only be obtained, however, from a detailed economic

comparison of the systems operating in realistic environments.

The value of this, of course, will depend

on the costs added in the process of providing tracking; this can only be resolved in

a detailed analysis of the relative costs of integrated systems.
Ch. VIII Collectors ● 3 0 1

Table Vlll-12.—Comparison of the Annual Output of Five Collector Designs, in kWh/m2

/year

Albuquerque Boston Ft. Worth Omaha

Annual radiation on nontracking flat plate tilted

at Iatitude. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual direct normal radiation . . . . . . . . . . . . . . . . . . . . . .

output of:

Single cover pond. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Tubular flat plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Commercial parabolic trough . . . . . . . . . . . . . . . . . . . . .

Improved parabolic trough design . . . . . . . . . . . . . . . . .

Heliostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fully tracking dish . . . . . . . . . . . . . . . . . . . . ... . . . . .

2,217

2,500

960

952

1,030

1,370

1,443

,481 1,742 1,665

,373 1,543 1,458

— — 630

538 705 619

529 621 561

720 835 765

791 887 833

1,901 1,023 1,150 1,085

SOURCE OTA

Table VIII-13. —Output of Single Cover and Double Cover Pond Collectors

for Various Operating Conditions

Mean collector temperature* = 90° F Mean collector temperature = 140” F—

Percent of output Percent of output

Annual output occurring during Annual output occurring during

(kWh/m

2

) October-March (kWh/m

2

) October-March

Single cover

pond collector

Double cover

pond collector

Albuquerque 958 23 447 13

Omaha 630 13 259 5

Albuquerque 804 24 470 16

Omaha 535 15 281 8

“It was assumed that the collector was operated with a constant fluld Inlet temperature I()” F lower than the mean collector temperature and a constarl~ output

temperature 100 F higher than the mean collector temperature

SOURCE OTA
Appendix VIII-A

Techniques Used to Compute the

Output of Representative Collector Designs

The major variables which must be con -

sidered in analyzing collector performance

were reviewed in a qualitative way in the

main body of this chapter. This appendix indicates how these effects can be quantified

and shows how the equations are derived

which were used to obtain the detailed estimates of collector performance presented

elsewhere in this report. Following the taxonomy of effects used in the earlier discussion, this presentation begins with a discussion of techniques for deriving estimates of

the intensity of direct and indirect sunlight

which can be captured by each collector

geometry. It then provides a detailed discussion of the optical and thermal losses experienced by each major colIector type.

AVAILABLE SUNLIGHT

Sunlight Data

As noted earlier, data about available sunlight around the country is of extremely uneven quality. Very few stat ions have measured direct normal sunlight, and results of

these measurements have not been readily

available. Information on the total amount

of solar energy reaching a horizontal surface is available from about 80 location s

around the country and is archived in the

National Climatic Center in Asheville, N.C.

While this data does not distinguish between direct normal radiation and diffuse

radiation, statistical techniques have been

developed which can be used to approximate the relative contributions of the two

types of radiation. The technique used in

this study is based on work completed recently by Sandia Laboratories.

‘ E Idon C Bees, Est/rnatjng the Direct Component of

So/ar /?adiat/or-r, Sandla Laboratories Energy Report,

SAND 75-0565, November 1975

The basis for the Sandia analysis is the

observation that the intensity of direct normal radiation is correlated with the ratio

between the amount of energy actuall y

reaching a horizontal surface in a given hour

and the amount of energy which would have

fallen on the surface if the Earth had no atmosphere. This ratio is called the “percent

possible” sunshine and will be represented

by the variable PP. The Sandia work compared the intensity of direct normal radiation (1D N

) as a function of PP in several locations where measurements of I DN were available. It was found that the relationshi p

could be approximated with a simple segmented straight-line formula which takes

the following form: (A-1 )

M

where A, B, C, and M are constants which

must be determined for each location. T h e

values of these constants which apply to the

three cities (for which consistent direct normal sunlight data is avaiIable) are shown in

table VII l-A-l. Notice that in Albuquerque it

was necessary to use different constants for

midday and periods early and late in the

day. In the analysis of sunlight data for Fort

Worth, average values of the constants were

used (A = 1.79, B = –0.55, C =0.85, and

M = 1.00).

The data actually used for the estimates

of collector performance conducted as a

part of this study was taken at weather stations during 1962 (1963 in Boston). Table

VII l-A-2 compares the average values of

direct normal, and total horizontal radiation

measured at these stations (and reduced us303
304 Ž Solar Technology to Today’s Energy Needs

Table VIII-A-1 .—Empirically Derived Constants

Used in the Formula for Estimating Direct

Normal Radiation, Given Measurements of Total

Horizontal Radiation (see equation A-l)

Spring Summer Fall Winter

Albuquerque*

Mid E-L Mid E-L Mid E-L Mid E-L

A 1.64 1.13 1.65 1.07 1.56 1.15 2.42 1.68

B -0.43 -0.19 -0.35 -0.17 -0.47 -0.21 -0.78 -0.25

C 0.85 0.85 0.80 0.80 0.85 0.85 0.80 0.80

M 1.07 1.07 0.95 0.95 0.97 0.97 1.09 1.09

Blue Hill

A 1.60 1.86 1.93 2.10

B -0.52 -0.56 -0.58 -0.71

c 0.80 0.70 0.75 0.80

M 0.89 0.81 0.87 1.03

Omaha

A 1.69 1.62 1.88 1.67

B -0.62 -0.50 -0.68 -0.48

c 0.85 0.80 0.85 0.85

M 0.89 0.87 0.96 0.98

“ln Albuquerque, It was necessary to have separate Sets of constants for mldday

(Mld)andearlyand late ln the day (E-L)

SOURCE Bees, Eldon, “Esttmatlng the Dlrecl Component of Solar Radiation,”

Sandla Laboratories Energy Report, SAND 75-0565, November 1975

ing the methods previously discussed) with

average values of these quantities for a 15-

year period. The 15-year averages were computed from data prepared by the National

Climatic Center and the Aerospace Corporation. The 15-year average values shown i n

the table contain correction factors which

compensate for calibration errors recently

discovered in some of the older measuring

equipment. While, as expected, the 1962

data does not precisely match the long-term

average, no systematic error is apparent—

some of the 1962 averages are higher while

others are lower than the 15-year averages.

Since observing sites a few miles apart can

take measurements of sunlight and temperature which differ by 10 percent during the

same year (because of microclimates producing local patterns of fog, etc.), the 196 2

data probably represent a reasonable estimate of insolation as it is reasonable to

make, given other errors inherent in projecting the cost of solar energy.

Direct Normal Radiation

The amount of direct normal radiation incident on a collector which is not directly

facing the Sun is reduced by a factor equal

Table Vlll-A-2.—Comparison of 1962* Weather With Long-Term Averages and Extremes

Average daily sunlight

(kWh/m2

/day) Albuquerque Boston Fort Worth Omaha

Direct normal 1962. . . . . . . . . . . . . . .

15+ yr av** ● . . . . . . . . . . . . . . . . . .

Ratio: average/1962. . . . . . . . . . . . . .

Total on horizontal surface, 1962 . . .

15 + yr av** . . . . . . . . . . . . . . . . . .

Ratio: average/1962. . . . . . . . . . . . . .

Heating degree-days† 1962 . . . . . . .

1954-74 average . . . . . . . . . . . . . . .

1954-74 extremes. . . . . . . . . . . . . .

7.0 3.9 4.3 4.0

7.1 3.3 4.7 4.5

1.01 0.85 1.09 1.13

5.5 3.7 4.5 4.2

5.8 3.5 4.7 4.2

1.05 0.95 1.04 1.00

4,310 5,754 2,434 6,272

4,374 5,769 2,423 6,145

3,857-4,941 5,410-6,228 1,861-2,855 5,622-6,911

“Read as 1963 for Boston wherever 1962 IS used

“” 15 + year average was compiled from the augmented SOLMET weather tapes produced by the National Cllmatlc Center and the Aerospace Corporation.

†Heatlng degree-day information from “Local Cllmatologlcal Data–Annual Summary with Comparative Data. 1974” Nattonal Cllmatlc Center, Asheville, N.C
Appendix VIII-A ● 30.5

(A-2)

must be considered, With the appropriate

choice of geometry, however, the actual calculation can be quite simple. A technique is

displayed here which permits a calculation

expressed in the same coordinates. The

coordinates which are the most convenient

are the “collector site coordinates” illustrated in figures VI II-A-I and VIII-A-2. A

glossary of symbols used in computing collector geometry appears in table VI 1 l-A-3. In

these coordinates, the z-axis points at the

zenith at the colIector site, the y-axis points

south in the plane of the horizon, and the xaxis points west in the plane of the horizon.

Figure VI II-A.1.– Collector Coordinates Showing the Collector Direction and

the Axis of Rotation of the Collector Direction

(Zenith)

z = z’
306 ● Solar Technology to Today’s Energy Needs

Collector

site

Earth’s

equator

x and x‘

Table Vlll-A-3.—Glossary of Symbols Used

in Computing Collector Geometry

(a) Variables describing the solar position

L

w

Te(n)

n

latitude of the collector site (north is positive)

solar hour angle (east is positive, due south is

zero)

solar declination (north is positive)

local standard time on nth day of the year

clock time using the applicable time zone of

the region (eg. eastern standard time) on the

nth day of the year

a correction of Tn called the “equation of time”

resuIting from the fact that the Earth’s orbit is

not circuIar, computed for day n

the day of the year (0 < n < 365)

(b) Variables describing the position of the collector

Y’

SOURCE. OTA

The first step is to obtain an expression for

the direction of the normal to the collector

illustrates a completely general collector

which are obtained by two rotations from

the x,y, z system: 1 ) a rotation around the zthe new x’-axis defined by the previous rotasingle-axis tracking system where y“ is the

axis of rotation. The vector can now be

transformed simply back to the x,y, z coordinates through two unit rotations which
reverse the rotations by which the x,y, z coordinates. With this transformation

(A-4)

The second step is to write the Sun posidone by examining figure VI II-A-2 which

These coordinates are obtained by rotating

the collector site coordinates x,y, z through

latitude angle). The z’ axis points to true

north. In these geocentric coordinates, the

Sun’s position can be computed simply from

function of the seasons, and the solar hour

be written in geocentric coordinates a s

follows:

This vector can be translated into collector

site coordinates with a simple unit rotation

about the x’ axis giving

(A-6)

Appendix VII I-A Ž 307

This achieves the objective of expressing

dinates and the cosine function can be computed:

Using equation A-7, the tracking geometry

of alI colIectors can be computed rapidly.

FLAT-PLATE COLLECTORS

The typical flat-plate collector i s

mounted on a sloping roof which face s

south, or nearly so. The general formula” for

a fixed fiat-plate collector which is tilted up

stead of with the horizontal). When the colSINGLE-AXIS TRACKING COLLECTORS

Single-axis tracking collectors can be

mounted many different ways, but two

widely used

in this study

Polar Mount

The polar

configurations have been used

mount provides more annual

output than other single-axis trackin g

mounts, but is generally more expensive to

construct than mounts where the rotational

axis is horizontal. The polar mount can be

visualized by imagining a collector which

rotates about a horizontal axis running from

north to south and then tiIting the rotational

axis up from the horizontal and toward the

south by an amount equal to the latitude

angle L (see figure VI 11-8). The cosine factor

for polar-mounted tracking devices can be
308 ● Solar Technology to Today’s Energy Needs

and 13 = L, the latitude angle. Using these

values in equation A-7 and minimizing the

result with respect to the collector angle of

cidence is then simply the solar declination

and

(A-8)

East-West Axis of Rotation

Collectors which rotate about a horizontal axis that runs east to west receiv e

somewhat less sunlight than single-axi s

polar-mounted collectors, but are sufficiently less expensive that they are more widely

used. The cosine factor for this collector

maximized with respect to the trackin g

(A-9)

gebra it is found that

(A-IO)

Equations of Time

The previous section showed how the collector cosine factor could be compute d

from information about the solar position

(the declination and hour angle) and the collector position. Solar declination can be

computed simply since it varies approximately sinusoidally from plus 23.5 degrees

to minus 23.5 degrees with the maximum occurring at the summer solstice. Computation

of the solar hour angle from local time is

complicated by two factors: 1 ) the time

shown on clocks with which the sunlight

observations are correlated does not correlate with local solar time since each time

zone covers a large spread of longitudes —

the Sun can not be due south at noon in the

entire time zone; 2) the times at which the

Sun is directly south are not separated by

precisely 24 hours (although the yearl y

average of these separations is exactly 24

hours) since the Earth’s orbit is an ellipse

and not a circle.

the nth day of the year in the local time zone

(i.e. eastern standard time) and TN(n) is the

time at which the Sun points due south on

this day (measured in the same local clock

time), the solar hour angle can be written on

this day as follows:

(A-1 1 )

The time for solar noon can be computed

from the latitude of the collector site (L), the

latitude to which the prevailing time zone is

referenced (Lref) (Lref is 120°W for Pacific

standard time), and a correction factor Te

(n)

computed for each day to account for the

elliptical nature of the Earth’s orbit. Using

these variables it is found that:

The equation of time is a complex function

of the day of the year and its specification

requires solving equations for which n o

closed solution is possible. It can be approximated to limits of precision compatible

with the rest of the analysis which will be

employed here with four terms of a Fourier

series. This series is expanded as a periodic

function of the length of the year since the

equation must have a period of precisely 1

year Coefficients of this expansion have

been computed by the National Bureau of

Standard s

2 and are illustrated in table

VII l-A-4. The Fourier formula is, as follows:

‘T. K usuda, NBSLD Computer Program

and Coo/ing Loads in Bui/dings, NBS I R

vember 1974

for Heating

74-574, No-
Appendix VII I-A ● .309

Table Vlll-A-4.— Coefficients of the Fourier Expansion

of the Equation of Time Used in Equation A-15

A O -0.0002 B 0 0

A l 0.4197 B1

-7.351

A 2 3.2265 B2-9.3912

A 3 0.0903 B3

-0.3361

Diffuse Radiation

The diffuse component of the solar radiation reaching a horizontal surface (I d h

) can

be computed if information is availabl e

about the total energy incident on a

horizontal surface (1 T H

) and the direct normal radiation ( 1D

).

the horizon directly below the Sun,

This equation, however, carries no information about the distribution of diffuse

radiation across the sky and thus there is not

a simple way to compute the amount of diffuse radiation that can be collected by a

device which is not horizontal, In fact, the

distribution of diffuse radiation over the sky

dome varies widely, depending on local

weather conditions and on the time of day,

It is remarkable, however, that there is very

little data in the literature about the distribution which can be expected. In the following discussion, the simplifying assumption

that diffuse radiation is distributed uniformly across the sky dome (the “isotropic

sky ” assumption) has been used, eve n

though it is known that under some conditions the bulk of diffuse radiation emanates

from a region in the sky close to the Sun.

Very recent work’ indicates that this is a

conservative assumption which understates

the radiation on a tilted surface by as much

as 7 percent.

‘Thomas M Klucher, Var/ation of 50/ar Cc// 5ensttt vlty and So/ar Rad/a tion on Inclined Surfaces,

presented at the Semiannual Review Meeting, ERDA

Slllcon Technology Programs Branch, Aug 23-25,

1977, Wllllamsburg, Va

Using this “isotropic sky” assumption, it is

possible to convert l

dh computed in equa -

tion A-1 4 into an estimate of i D

-- the intensity of diffuse radiation on a tilted collector.

Following Liu and Jordan, ’ it is assumed that

the diffuse radiation reaching the collector

consists of two parts: (1) a part received

directly from the sky (which is assumed to

radiate isotropically) and (2) a part reflected

from the ground (which is proportional to

the fraction of the sky from which radiation

could be reflected into the collector). Using

these assumptions, it is possible to compute

i

d for a collector which has been tilte d

ground. The reflectivity varies greatly from

location to location. It may be very high if

the area is covered with snow, and it can be

artificially enhanced by placing ponds, or

reflective surfaces, in appropriate locations

close to the reflectors. For the purpose of

this analysis,

which is a typical reflectivity of dry ground.

Optical Losses

in addition to the limits imposed by the

geometry of tracking, the amount of light

which reaches the receiver units in solar collectors is limited by a number of losses due

to imperfect optics. These losses include: 1)

energy absorbed by transparent covers ove r

the receiver; 2) losses when light is reflected

from mirror surfaces or transmitted through

lenses; 3) errors in pointing a tracking collector at the Sun; and 4) shading of collectors

by adjacent collectors, or (in the case of

4 B Y H LIU and R C Jordan, “The Long-Term Average Performance of Flat-Plate Solar Energy Collectors,” So/ar Energy 7, 53(1963)
310 ● Solar Technology to Today’s Energy Needs

some tracking units) by other parts of the

collector. Designing an optimum collector

requires balancing the features which can

improve optical efficiency against other

design constraints. For example, adding

cover glasses can reduce thermal loss but increase optical losses. Increasing the focal

length of a concentrating collector can reduce dispersion and transmission losses in

lenses, but increases the size of the Sun’s image and can add to the bulk and contribute

to the wind profiIe of the collector. 5 Increas -

ing the concentration ratio decreases thermal losses, provides a higher temperature

thermal output, or reduces the amount of

photovoltaic material required. Higher concentrations increase the significance o f

pointing errors.

TRANSMISSION LOSSES

Light is lost when it passes through transparent receiver covers. Some light is lost due

to surface reflections (from both the front

and back surface of the covers), and some

light is absorbed by the transparent material. These losses represent the bulk of optical losses in flat-plate collectors and can

play a significant role in concentrating collectors which surround a receiver with a

glass or plastic cover.

The transmission coefficient for various

types of materials is illustrated in table

VII l-A-5. These losses are computed only for

normal incidence, however, and transmission decreases with increasing angles of incidence. The analysis of the transmission at

angles of incidence other than zero can be

complex. The following formula fits empirical data with a fair degree of accuracy:6

5Gene Nixon, cast acry/ic Fresne/ /ens so/ar concentrator distributed by Swedlow, Inc., obtained by OTA,

May 26, 1977.

‘Empirical expression provided for OTA by Don

Watt

T(0) is the transmissivity for a case where the

light is incident normal to the plane of the

cover. If diffuse light strikes the collector

averaged over the section of the sky which is

viewed by the colIector as follows:

(A-1 7)

by the collector.

For a horizontal fIat-pl

e of the sky viewed

ate system receving

radiation from an isotropic sky, equation

A-1 8 gives:

T (one cover) = 0.89 T(0)

T (two covers) = 0.80 T(0) (A-18)

IMPERFECT REFLECTIONS FROM

MIRROR SURFACES

Materials proposed for use as mirror surfaces in concentrating collectors var y

greatly in their cost and optical properties.

An ideal material would be inexpensive,

have a high reflectance, create little dispersion (i. e., a narrow beam of incident light

should be reflected without spreading),

resist impact from hailstones (no fracturing

or denting), and not attract dust. Candidate

materials include first-surface glass mirrors

(which have high reflectivity but are vulnerable to tarnishing and scratching), secondsurface glass mirrors (low-iron glass is preferred to reduce absorption), second-surface

bulk acrylic mirrors, annodized aluminum

(relatively inexpensive and easy to form but

a lower overalI reflectivity (60 to 80 percent)), and a variety of metalized plastic

films. The plastic films are much less expen-
●

Appendix VII I-A . 311

Table Vlll-A-5.—Transmittance of Transparent Covering Materials

Which May be Used in Solar Collectors

(Assuming the Solar Spectrum Resulting From Air Mass 1)

cutoff Normal

Thickness wavelength Hem is, solar

Material (in. ) Supplier um refIectance transmittance

Quartz . . . . . . . . . . . . . . . . . . . . 0.125 Sandia 0.26 0.064 0.94

Glass Shop

Teflon 100 C . . . . . ., ... . 0.001 Dupont 0.26 0.031 0.93

Pyrex (Corning 7740) . . . . . . 0.134 Sandia 0.36 0.067 0.91

Acrylite ., ., ... ., ., ., . . . . .

Plexiglas “G” ., ., ., ., ., ., .,

0.0625

0.125

0.0625

Glass Shop

Petterson

Petterson

0.35

0.35

NM†

NM

0.89

0.87

0.88

0.219 0.86

Tedlar, polished. . . . . ., . . . 0.004 Dupont 0.31 0.080 0.88

Swedlow centinuous

cast acrylic. . . . . . . . 0.076 Swedlow 0.33 0.070 0.88

Swedlow coated acrylic, . 0.273 Swedlow 0.39 0.058 0.85

cell cast

Israeli collector glazing ., . . 0.092 Peterson 0.31 N M 0.85

Glass for mirror . . . . . . . . . . . . . 0.125 Champion 0.31 0.070 0.85

cutoff Hemispherical

Thickness wavelength Hem is. solar

Material (in. ) Supplier um refIectance transmittance —

Teflon 100 C . . . . . . . . . . . . . 0.001 Dupont 0.25 0.031 0.96

Aclar #22A . . . . . . . . . . . 0.002 Rain hart: 0.25 0.060 0.94

Allied Chem.

Corning Ultramicrosheet . . . . . 0.0045 Butler: Corning 0.30 0.071 0.92

Tedlar, polished. . . . . . . . . 0.004 Dupont 0.30 0.080 0.91

Lucite 147 ... . . . . . . . . . 0.120 Dupont 0.38 NM† 0.85

Mylar D. . . . . . . . . . . . . . . . . . . . 0.010 Dupont 0.33 0.112 0.85

Rhom-Haas Korad A. . . . . . . . . 0.005 Brumleve 0.38 0.088 0.86

std. clear

Fllon A748, Tedlar coated, ... , 0.028 Filon Corp. 0.38 0.082 0.84

Kalwall Sunlite Regular . . . . . . 0.040 Kalwall Corp. 0.38 0.079 0.83

Mylar A. . . ., ... . . . . . . . 0.005 Dupon 0.38 0.19 0.78

Kalwall Sunlite Premium . . . . 0.040 Kalwall Corp. 0.38 0.087 0.79

Swedlow continuous .. . 0.076 Swedlow Corp. 0.38 0.070 0.86

cast acrylic

Swedlow coated acrylic . 0.273 Swedlow Corp. 0.38 0.058 0.85

(cell cast)

— .-

†NM = not measured

SOURCE Solar Total Energy Program Se~laflflu~/ RePort April 1975 September 1975 SAN D76 0078 Sandla Labs, Albuquerque N Mex Apr!l 1976 p 98 99
372 ● So/ar Technology to Today’s Energy Needs

sive, but many appear to age rapidly and to

attract dust, and currently available materials have relatively low reflectivities. The

search for an optimum reflecting surface

will be an important development problem

for the next several years.

Figure VI II-A-3 and table VI II-A-6 illustrate the optical properties of a number

of different reflecting surfaces. It can be

seen that the materials vary greatly both in

total reflectivity and in the amount of dispersion introduced. The reflectivity for glass

mirrors can be as high as 96 percent, while

the inexpensive aluminum reflectors can

have refIectivities below 80 percent.

The surfaces also vary in the amount of

dispersion which they introduce. Mirrors

which introduce large amounts of dispersion

cannot be used to achieve high magnification (as is shown quantitatively in the next

section). The aluminized 1 Mil Teflon film

material shown on figure VII l-A-3, for example, reflects 75 percent of the light incident

on it into a cone smaller than 4 mrad wide.

The second-surface glass mirror reflects

over 90 percent of its Iight into a cone less

than 2 milt-ad in width.

A final difference between surfaces is the

variation of reflectance with the angle of incidence of the incoming Iight. Class mirrors

and first-surface aluminized du Pont experimental film show almost no variation over a

wide range of incidence angles, while other

materials such as the aluminized 1-3 Mil

Mylar-S film have very poor reflectance at

small angles of incidence, 7

SHADING, BLOCKING, AND END LOSSES

Three additional loss factors must be considered:

7R. C Zenter (Boeing Aerospace Co ), “Performance

of Low Cost Solar Reflectors for Transferring Sunlight

to a Distant Collector, ” So/ar Energy, Vol 19, No 1,

1977, pp 15-21

Figure VI II-A-3.—The Specular Reflectance at 500nm as a Function of the Collection

Angular Aperture for Several Reflector Materials, Together With

80 -

60 “

40

20

B
Appendix VII I-A ● 3 1 3

Table Vlll-A-6.—Specular Reflectivities

Cone

Wavelength Specular angle (MRAD)

Material Supplier (um) Reflectivity containing Reference

67% of

reflected Iight

1. Second-surface

silvered glass Carolina

A. Laminated glass . . . . . Mirror Co.

B. Corning Microsheet, 0.11 mm. . . . . . Sandia

C. Corning 0317, no

iron, 1.5 mm fu - Carolina

sion glass. . . . . Mirror CO.

D. Float glass with

iron . . . . . . . . . . . . . ——

Il. First-surface glass

A. Double acrylic

coat, silver . . . Sheldahl

B. AL/ground glass

overcoat . . . . . . .

Ill. Polished aluminum

A.

B.

E.

ALZAK lighting

sheet

(Parallel to rolling

marks) . . . . . . . . . . . . Alcoa

(Perpendicular to

rolling marks). . . . .

KINGLUX reflector

sheet

(Parellel to Kingston

rolling marks). . Industries

(Perpendicular to Kingston

rolling marks). . . . . . . Industries

Household foil . . . . . . ——

V. Metalized plastic films

A

B.

c.

D.

E.

2nd-surf. alum.

FEK-163 . . . . . . . . . . . 3M

2nd-surf. alum.

Teflon . . . . . . . . . . . . . Sheldahl

2nd-surf. alum.

Teflon laminated

to alum. sheet . . . . . . Sheldahl

Al/nylon, 1st surf ., . ———

A1/Kapton-H, 1st

surf. , 0.25 mm . . . . . .

500 .92 0.15 (3)

550 .78 1.1 (4)

— .96 small (2)

— .82 smalI (2)

550 .93 .21 (4)

628 .88 <1.7 (6)

505

505

498

498

Sun

Sun

.62

.56

.67

.65

.81

.65

.29

.42

,43

.37

——

——

(3)

(3)

(3)

(3)

(8)

500 .86 0.90 (3)

500 .80 1.3 (3)

550 .87 1.2 (4)

Sun .80 — — (8)

628 .87 5 (6)

References

1 Handbook of Chernlsfry and Physics The Chemical Rubber Co , Ed by R C Weast, 54th Edlflon, 1973-1974, p E225

2 L G Ralnhard (Sandla Labs, Albuquerque) private communtcatlon, Aug 10, 1977

3 R B Pettt and B L Butler (Sandla Labs, Albuquerque) Sern~annua/ Rev(ew ERDA Therrna/ Power Systems, Dispersed Power Systems, f)jsfr~bufed Co//ec(ors

and Research and Deve/oprnent, Mirror Ma ferla/s and Se/ecf(ve Coatings SAN D7701 11, February 1977, p 6

4 So/ar Tofa/ Energy Program Sernlannua/ Report October 1975 and March 7976 SAND76 0205, Sandla Labs, Albuquerque, June 1976

5 Test report by Desert Sunshine Exposure Test, Inc , March 4, 1977, rendered to Kingston Industries Corp DSET Order No 17127S

6 R C Zentner (Boeing Aerospace Co ), “ Performance of Low Cost Solar Reflectors for Transferring Sunllg h! to a Distant Collector, ” So/ar Energy, Vol 19, No

1, 1977, Pp 15-21

7 L Drummeter and G Haas “Solar Absorptance and Thermal Emlttance of Evaported Coating s,’ Physics of Th(n FI/rm, 2, 1964 Ed by G Haas and R Thun,

Academic Press

8 F Damels (Umverslty of Wlsconsln, dec ) L7(recf Use of fhe Sun Energy Yale Untverslty Press of Ballantine Books, Inc 1964
314 Ž Solar Technology to Today’s Energy Needs

1.

2.

3.

“End losses” of one-axis tracking devices which result from the fact that

some part of the light reflecting from a

trough or other one-axis tracking unit

will miss the receiver surface except

during the infrequent occasions when

the incident light is directly normal to

the colIector plane;

Shading of collectors by adjacent collectors; and

Blocking of the reflected beam of a

heliostat by other heliostats

End Losses

If the collector reflecting surface is a flat

Fresnel lens or a series of coplanar linear

slats, light incident on an area of the collecreceiver surface. (F is the focal length of the

angle of incidence of direct sunlight measured with respect to a direction normal to

the plane of the collector. ) If the collector

length is L, then the fraction of the incident

light lost in end effects (1’,(0)) is given by:

(A-19)

If the system uses a parabolic trough, the

calculation is somewhat more complex

since points on the edge of the trough are

farther from the focal line than points at the

base of the trough. It can be shown that in

this case the fraction of the incident light

lost in end effects is given by:

where f = F/D is the “f-number” of the optical system.

Shading Factors

The amount of energy lost

Iector shades an adjacent coll

on the exact geometry of the

when one colector depends

collector field

and must be computed separately for each

case. These losses can be reduced or eliminated if the collectors are widely spaced,

but such separation increases the demand

for land use and can increase piping costs (in

the case of distributed collectors) or add to

the demands placed on pointing accuracy

(in the case of heliostat designs). In addition,

the solar image will be larger from more distant heliostats, decreasing efficiency, or

concentration ratio. A balance must b e

struck in each application. In many cases,

however, a shading problem will be negligible if the collector surfaces cover less than

about one-fourth of the area provided for

colIectors.

Heliostats

The shading, blocking, and cosine factors

of heliostat fields are complex since the

location and pointing angle of each heliostat in a large field must be analyzed to develop an estimate of overalI system performance. An independent analysis of this

problem has not been attempted in this

report and the computations of heliostat

performance rely on an analysis performed

by the University of Houston in connection

with the McDonnelI Douglas design proposal for a 10 MWe pilot plant for a 1 0 0

MWe central receiver system. The results of

this analysis are illustrated in figure VII l-A-4.

The curves shown include the effects of atmospheric attenuation for clear days in the

southwest United States, and apply to a

field optimally designed for a site at 350 N

latitude. The designers attempted to design

a system which performed well during the

periods near dawn and dusk, and which minimized seasonal variations. Mirror spacing is

not uniform, but on the average about onefourth of the area is actually covered with

mirrors.

The curves of figure VII l-A-4 indicate the

normalized power to the receiver and i n -

clude the cosine factors of the heliostats,

shading and blocking effects, a receiver interception factor, and attenuation between

the mirrors.
Appendix VII I-A ● 3 1 5

Figure VIII-A-4. —Monthly/Hourly Variation in Available Thermal Power

1.0

Day number range

Curve when the curve

number is applicable*

1 158-186

2 127-157 and 187-217

3 97-126 and 218-248

4 66- 96 and 249-278

5 36- 65 and 279-309

6 5- 35 and 310-340

7 1- 4 and 341-365

*January 1 is day #1

SOURCE Raymon W Hallet, Jr and Robert L Gervals. Central Recewer Solar Thermal Power System Phase I lst”Quarter Technical Progress Report McDonnell Douglas Astronautics Company (January, 1976), p 18 MDCG6318

These curves were used in the analysis by

approximating each curve with a six-Iine segment polygon adjusted so that the area

under the polygon was approximately equal

to the area under the curves illustrated. The

shapes of the polygons were also adjusted to

reflect different day lengths at latitudes

other than 35° N

Limits on the Geometric Concentration Ratio

The amount of concentration of sunlight

possible with a given set of optics is limited

by the pointing accuracy of the tracking

system used, by the dispersion introduced

into the optics by imperfect refIecting surfaces, and by the finite diameter of the Sun.
316 ● So/ar Technology to Today’s Energy Needs

(The intensity of the light actually reaching

the absorber will, of course, also be limited

by the cosine factor, shading and blocking

effects, and the reflection and absorption

losses discussed earl ier.)

There is some abiguity about the proper

way to define the geometric concentration

ratio. I n the following discussion, geometric

concentration ratio (Cg

) is defined to be the

ratio between the aperture of the colIector

and the area of the receiver which can be

reached by the reflected or refracted sunlight. This definition assumes that the portions of the receiver which can never be illuminated are well insulated. This definition

must be applied with some care in the case

of one-dimensional tracking systems since

the concentration ratio will not be equal to

the ratio between the solar energy reaching

the mirror or lens surface and the light

reaching the collector absorber (assuming

perfect optics), except when the Sun’s direction is directly normal to the plane of the

collector. At all other times, the effective

geometric concentration ratio for a perfect

collector is equal to the geometric concentration ratio multiplied by the shading factor 1

If the optical properties of the system are

perfect, the only limit on the geometric concentration ratio will be the angular diameter

from 9.16 milrad to about 9.46 milrad,

changing as the Earth-Sun distance varies

over the year. The limits which this imposes

on the concentration ratios possible are illustrated for three different concentrating

systems in figure VII l-A-5. The solar image

reflected (or transmitted) from an extreme

edge of the lens or mirror has a width of

transmitted) from the center of the lens or

(where F is the focal length of the optical

system). It can be seen that the intensity of

the image will be greater in the image center. This can create difficulties if “hotspots” place high stresses on small parts of

the receiver, and nonuniform illumination

can reduce the performance of photovoltaic

cells. With careful design the impact of

these effects can be reduced. For example,

the facets of a Fresnel lens or mirror can be

adjusted to spread the image to create a uniform illumination on the receiver surface.

Measurements performed on a cast acrylic

Fresnel lens designed by Swedlow, Inc., are

shown in figure VII l-A-6. CarefuI mirror

design or the use of a secondary mirror near

the focal point can also minimize the problem of uneven illumination. A precise computation of the intensity distribution of the

solar image requires compensation for the

fact that the luminosity of the Sun varies

over the solar disk. 8

The size of the solar image reaching the

receiver in any practical system will be

larger than the angular diameter of the Sun

because of dispersion introduced by imperfect reflecting or transmitting surfaces, by

imperfect concentrator shape, and because

of imperfect tracking. In addition, atmospheric dispersion (e. g., hazy sky) can increase the apparent diameter of the Sun by

a factor of 2 or more.

The dispersion introduced by different

types of reflecting surfaces was illustrated

in figure VII l-A-3. I n the following calculations, the cone angle containing 90 percent

Lenses have some advantage in minimizing

dispersion since an imperfection in a mirror

surface which has the effect of tilting the

mirror surface by an angle A above the ideal

mirror angle will result in an error 2A in the

angle at which light is reflected. A lens with

a similar error at each surface typically results in an angular error of less than 2A, depending on the index of refraction of the

lens and the angle between the lens surfaces.

Tracking errors can be treated with fair

accuracy by simply assuming that the solar

image is spread by tracking errors by an

‘D. L. Evans (Arizona State University), “On the Performance of Cylindrical Parabolic Solar Concentrators with Flat Absorbers, ” So/ar Energy, Vol. 19, No,

4,1977, Pp 379-385.
Appendix VII I-A ● 317

mane on Three Typical Concentrating Collectors

SOURCE OTA

angle at. The angle a t will be chosen to be

twice the angle between the ideal collector

direction and the actual collector direction,

which is exceeded less than 5 percent of the

time when the collector is operating. An estimate of the maximum concentration possible given tracking and optical dispersion efIf chromatic aberation is an important effect, ad should be increased accordingly. A

simple tracking system can achieve a pointing accuracy such that at is below about 0.5

degrees or 8.6 milrad. Such a system could

have a dispersion angle of 0.6 degrees or

10.5 milrad. A carefully constructed system

dispersion and tracking, of 6 milrad. 9 If the

mean solar diameter is used, these cases

‘Raymon W Hallet, Jr , and Robert L Cervals, Central Receiver Solar Thermal Power System Phase 1,

Fina/ Report, McDonnel I Douglas Astronautics Company (1 977) SAN 1108

Flat Fresnel Lens

with Cylindrical Absorber

give a = 16.5 milrad (imprecise optics and

where f = F/D and the other variables used

are defined in figure VII I-A-5, It will also be

(see figure VIIl-A-5). This variable can be

computed from R m

/D as follows:
318 ● So/ar Techno/ogy to Today’s Energy Needs

Figure Vlll-A-6.— Characteristics of the Image of Acrylic Fresnel Lenses Designed

by Swedlow Inc. for Solar Applications

Intensity distribution at the focus of an acrylic fresnel lens designed for

one-axis concentration on a Iinear thermal receiver.

two-axis concentration on a photoelectric device. -

600

500

400

300

200

100

SOURCE Nixon Gene Cast AcrylIc Fresnel Lens Solar Concentrator paper distributed by the Swedlow Inc obtained

by OTA May 26, 1977 pages 27 and 22
(A-22)

With perfect tracking and optics, all of the

sunlight incident on a one-axis tracking colIector could be captured by a flat receiver

with area Ar where

(A-23)

In computing the effective receiving area

for a receiver with a circular cross section, it

is assumed that the portions of the receiving

tube which are never ilIuminated by the Sun

are covered with an insulating material of

sufficient quality that losses through the insulation are negligible, The angle measured

from the center of the circular receiving

by

fraction of energy lost as end losses

fraction of energy lost in shading

and blocking

refIectivity of mirrors

transmissivity of cover plates

angle of solar incidence on collector

angle between zenith and Sun

colIector tiIt above horizontal

surface reflectivity of the ground

direct sunlight

total horizontal sunlight

As the concentration ratio increases

above one, the fraction of the diffuse radiation intercepted by the collector which

reaches the receiver surface drops rapidly,

and for concentration ratios above 10, the

diffuse sunlight can generally be neglected,

Ieaving

Thermal Losses

Not all of the solar energy reaching the

receiving element of a solar colIector can be

removed as useful energy since some of the

energy reaching the receiver wilI be reflected from the absorbing surfaces of the

receiver and some of the absorbed energy

will be conducted or reradiated back to the

atmosphere. As shown earlier, the thermal

loss effects are usually much more significant for flat-plate collector systems with

relatively large receiver surfaces than they

are for concentrating systems with relatively
320 ● Solar Technology to Today’s Energy Needs

Table Vlll-A-7.—Maximum Possible Geometric Concentration Ratios at Perihelion

—— .

1 -D Concentrator 2-D Concentrator

SOURCE. OTA

Table Vlll-A-8.—Maximum Possible Geometric Concentration Ratios

1 -D Concentrator 2-D Concentrator ——

● ☛✎✎☛✎☛✎☛✎

2140,

3449.

3023.

2378.

1849.

1455.

1164.

948.

785.

660.

561.

483.

419.

368.

325

289

259,

233.

211

.-

1330

1553.

1257,

952

725.

565.

450.

366

303.

255.

217

187.

163.

143,

126.

113.

101

91

83.

75 —

1640

3283.

3337.

2787

2207.

1739.

1384

1118

917.

764

644

550.

474,

413

363

321.

286

256

231

209

.

SOURCE OTA
small receiver surfaces. The thermal loss ef -

fects have been treated extensively in a

number of recent publication s

10 11 12 13 14 15

and no attempt is made to reproduce the

analysis presented in these works. All that is

done here is to summarize the results which

are directly relevant to the analysis of this

study.

THERMAL LOSSES AND HEAT COLLECTED

Two different, but rather simple, expressions were used to compute the thermal

losses, For some cases, the fluid flow rate fr

was fixed. The heat QC colIected per unit

area of colIector is then

Here UL is a thermal loss coefficient (the effective conductivity between the heate d

fluid and the atmosphere). Fr is the “collector heat removal factor’’” which accounts

for the use of the fluid inlet temperature T,

instead of the mean absorber temperature in

the calculation. Ta is the outdoor air temperature.

The other case modeled assumed that the

flow rate is varied so the fluid outlet tem-

‘“John A Duffle ancf Wllllam A Beckman, op clt

chapters 4-8

1‘ Frederick F .51mon, F/at-P/a?e Solar-Col/ector Performance Evaluation with a Solar Simulator as a Basis

for Co//ector Selection and Performance Prediction,

NASA TM X-71 793, presented at 1975 ISES Meeting,

Los Angeles, Callf

1‘M W Eden burn, Performance of a Focusing Cylindrical Parabolic Solar Energy Col)ector: Analysis and

Computer Program, SLA-74-0031, Sandia Laboratories,

Aprl I 1974

‘‘G W Treadwell, W H McCulloch, and R S

Rusk, Test Results from a Parabo/jc-Cy/indrica/ So/ar

Co//ector, SAND 75-5333, Sandla Laboratories, July

1975

14 Raymon W Hal let, J r , and Robert L Gervais, Central Receiver Solar Power System, Phase 1– Final

Report PI/et P/ant Pre//minary Design (MCDG 6040),

pp 310, 337,366, j anuary 1976

1‘Giovanni Franc la, “Large Scale Central Receiver

Solar Test Facilities” Proceedings, I nt Seminar on

Large Scale Solar Energy Test Facilities, Las Cruces, N

Mex , Nov 18-19, 1975

“John A Duffle, op clt pp 146-151

perature TO remai

Iected is then

Appendix VII I-A ● 3 2 1

ns constant. The heat col-

(A-28)

Here ke is the thermal conductivity between the absorber surface and the fluid,

For the concentrating collectors considered,

U L

/ ke is less than 0.01 and can be ignored.

For heliostats, UL was based on the outlet

temperature rather than the mean temperature.

Typical thermal loss coefficients for a

variety of collectors are shown in table

VII l-A-9.

It should be noted that the thermal loss

term of equation A-27 would be divided by

the concentration ratio to obtain the heat

lost by concentrating collectors. The expressions used for determining the performance

of photovoltaic collectors are somewha t

more complicated and are discussed i n

chapter X.

Detai/ed Ca/cu/ation of F/at. P/ate Co//ector Output

This section presents methods for computing the output of flat-plate collector s

which assume that the thermal loss coefficient UL is constant and a method which explicitly considers the dependence of UL o n

the wind velocity, collector tilt, absorber

temperature, and air temperature. The results show that the approximations used

with UL constant are adequate for the longterm system performance which is central to

this study.

There are three primary sources of heat

loss from the receiver of a solar collector:

1.

2.

Radiation – Any hot body radiates enertemperature of the body in degrees Kelconstant:

(5.67 x 10-8Watt/m2-K4).

Conduction – Heat flows from th e
322 ● So/ar Technology to Today’s Energy Needs

3

Table Vlll-A.9.—Typical Thermal Loss Coefficients

Collector type (kW/m2

°C) Temperature range Reference

1 cover flat plate . . . .0074 < 150° F ( < 66” C) 1

2 cover flat plate . .0046 -.0063 < 200° F ( < 93” C) 1

2 cover fIat plate,

selective absorber. . .0032 -.0046 < 250° F ( <1210 C) 1

Tubular flat plate. . .0011 -.002 < 250° F ( <121 “C) 1,2

Parabolic trough,

unglazed. . . . . . . .025 140°-3500 F (60°-1770 C) 3

Parabolic trough,

glazed, sel.

absorber, no .009 250°-6000 F (121 0

-3160 C) 4

vacuum. . . . . .

Heliostat . . . . . . . . . .03 9000-1 ,100° F (482°-5930 C) 5,6

Parabolic dish . . . . . . .076 1,4000-1 ,500° F (760°-8160 C) 7

1 Simon, Frederick F , op clt

2 A/r Corrdltlonirtg & Refrlgerat(on Bus/rress, July 1976 data for KTA collector

3 Acurex Aerotherm, “Technical Note, Concentrating Solar Collector Model 300201 ,“ received by OTA, 1977

4 Acurex Aerotherm, “Model 3001 High.Temperature Concentrating Solar Collector, ” speclf{catlons received by OTA, 1977

5 Hallet, Raymon W , Jr Ib{d

6 Franc la, Glovannt, Ibid

7 Estimate based on T’ scahng of heliostat value

heated collector surfaces through insulation, covering glass, and structural

supports to the atmosphere.

Convection – Circulation of the air between the collector plates or motion of

air outside the top cover of the collector causes thermal losses. Such circulation is generally present due to gravity,

even in enclosed spaces. Such losses

can, of course, be greatly reduced if the

space between the receiver surface and

covers is evacuated.

For long-term modeling, the heat loss can

be treated as proportional to the difference

between the average absorber surface temperature and the ambient air temperature;

i.e., the heat loss per unit absorber surface

ductance between the absorber surface and

the atmosphere and includes losses due to

al I three processes mentioned above.

When the collector inlet and outlet fluid

temperatures T, and TO are known, th e

useful thermal output (QC

) can be given as:

(A-29)

colIector aperture area

sunlight intensity reaching the collector (see equation A-25)

thermal loss coefficient per uni t

area of absorber surface

concentration ratio of the optical

system used

the ambient air temperature

heat transfer coefficient between

the absorber surface and the fIuid,

Equation A-29 makes the implicit assumption that the temperature of the surfaces of

the absorber and the fluid temperatures

vary I i nearly over the area of the collector.

The actual distribution of temperature s

across the area of the collector depends on
Appendix VII I-A ● 323

the details of the construction of the device

(placement of the tubes, the heat-conducting properties of metal surfaces, etc.).

Several recent papers have examined this

problem with some care ,

17 18 19 A simpl e

technique for approximating this complicated calculation which was used in the

analysis conducted for this study relies on

defining a correction factor, Fr.

This correction factor, sometimes called

the “heat removal factor, ” is defined to be

the ratio of the useful thermal output of a

colIector (Qc) to the usefuI output of the collector, assuming that the entire collector absorber surface was held at the inlet temperature (T,):

(A-30)

where fr is the mass velocity of the fluid

moving through the collector and CP is the

specific heat of the collector fluid. The heat

removal factor defined in this way actually

changes slightly throughout the year as a

function of operating conditions, but it can

be shown that in most cases of practical interest, these changes are negligibly small

when T O

- Ti is only a few “C. Assuming that

‘‘F F Simon, F/at-P/ate So/ar Co//ector Performance

Evaluation Performance Pred/ct/on, presented at the

ISES Meeting, Los Angeles, Cal If , )uly 28-Aug 8, 1975

‘

8 Duffle, op clt , pp 138-153

“E M Sparrow and R J Krowech, /ourna/ of Heat

Transfer, Vol 99, 1977, pp 360-366

F R is a constant, the collector output can be

given as follows:

Techniques for computing F R for different

types of collector geometries are discussed

in detaiI in Duffie.

2 0

A similar approximation which can b e

used to evaluate the performance of collectors covered with photovoltaic cells is

discussed in chapter X. The values of UL a c -

tually used in the analysis were based on the

empirical performance data summarized i n

table VII I-A-IO.

An iterative Solution to Collector Heat Loss

A typical flat-plate collector is shown in

figure VI II-A-7 and is used to illustrate the

detailed method used to compute hea t

losses. The system is characterized by five

temperatures:

the temperature of the absorber

plate

the temperature of the inside cover

the temperature of the outside

cover

the ambient air temperature

the effective black body temperature of the atmosphere

20 Duffie, op cit., pp 146-151

Table Vlll-A-10.—Ratio of Collector Output When “Average” U-Value Used to Output of Collector

With Variable U-Value for Flat-plate Collectors in Omaha With Tilt Angle— Latitude

Collector Inlet “Average”

type temper- U-value Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

ature (kW/m

2

°C)

1 cover 90° F(32°C) ,0069 .946 .954 .977 .999 1.007 1.005 1.005 1.0031.002 .999 .992 .970 .996

1 cover 120°F(49°C) .0072 .900 .913 .964 1.006 1.033 1.024 1.0191.0221.014 1.003 .993 .942 1,004

2 cover 120°F(49°C) .0041 .945 .956 .974 1.001 1.015 1.012 1.011 1.0121.007 1.002 .989 .967 .998

2 cover, 1 50° F(66°C) .0025 .978 .983 .991 1.004 1,014 1.012 1.011 1.011 1.007 1.004 .999 .986 1.003

selective

absorber

SOURCE OTA
324 ● Solar Technology to Today’s Energy Needs

Figure VIII-A-7. —Geometry of a

Simple Flat-Plate Collector

(The typical temperature drop occurring

across a glass cover is less than 10 C, so each

cover is assumed to be at a single temperature. ) The receiver and first cover are separated by a distance d12 and the inside and

outside covers are separated by a distance

d 23. In equilibrium, the heat flowing from

the absorber to the first cover must equal

the heat flow between the two cover plates

which must, in turn, equal the heat flowing

from the top plate into the atmosphere. If

the heat flowing from surface i to surface j is

called Q ij, the heat flows can be expressed

Here hij are the effective convective/conductive heat transfer coefficients (it being

assumed that convective and conductive

losses are linear with the temperature differradiative heat transfer between the two

surf aces.

supposing that energy radiated from one

is all incident on a second surface with temreflected. An infinite series can thus be constructed and it can be shown that the net

heat transfer rate per unit area is given by

The convective/conductive heat transfe r

coefficients are much more difficult to evaluate since a number of effects can contribute to these losses and since the convective

effects will depend on the precise geometry

and orientation of the collector. The coefficients which apply to the spaces inside the

colIector (h12 and h23 ) are usualIy given by:

(A-34)

ess (the ratio of the convective heat transfer

to the conductive transfer) and Ka is the conductivity of air. The problem then become s

one of establishing an appropriate Nusselt

number for the process. Hollands, et al.,

21

have suggested the following (basically empirical formula):

‘

l K,G. T Hollands, et al., )ourna/ of Heat Transfer,

Vol. 98, May 1976, pp. 189-193,
Appendix VII I-A ● 3 2 5

Rayleigh number

thermal expansion coefficient of air

kinematic viscosity of air

gravitational acceleration

thermal diffusivity of air

angle of tiIt from horizontal

T i+1 – Ti

“E M Sparrow, University of Minnesota, private

communication, Febr 25, 1977

“J R Lloyd, E M Sparrow, and E R C Eckert, Int.

journal of Heat and Mass Transfer, 15,457-473, (1972)

cuss ion since they are easy to compute once

the temperatures in the colIector are known,

Since the heat loss coefficients kij have a

weak but complicated temperature dependence, it is usually not possible to obtain a

closed expression for UL

. The most convenient technique for computing U L is to solve

an algorithm for the expression using a

I digital computer. One such technique is

presented below,

The solution is initiated with the assumption that the average temperature of the

receiving surface (Tl

) is equal to the inlet

fluid temperatur e T, and that the

temperature rise across the thickness of the

colIector is equalIy divided between the two

=

then be used to compute the heat loss coefficients kij which can in turn be used to obtain a new estimate for the temperatures T3

and T2 using equation A-32. These new temperatures can then be used to compute a

new set of approximations to kij. The cycle is

continued until successive values of T2 a n d

T 3 satisfy a convergence criteria. When the

desired convergence is achieved, the parameter U'L can be computed, including the side

and back losses. This U'L can be used to compute the collector output:

and the output temperature of the flui d

moving through the collector is then T O = Tj

and CP is the specific heat of the fluid, With

this estimate of TO, a new estimate of the

average temperature of the colIector surface can be computed as (T, + T O

)/2 +

ficient between the fluid and the absorber

surface. The procedure for computing U L for

a given ambient temperature and plate temperature can be used again to obtain a new

estimate of UL

. This series can be continued

until a convergence criteria for the average

temperature of the collector surface is satisfied. A final value of U' L can then be computed which meets all of the specifie d

boundary conditions.
326 ● Solar Technology to Today’s Energy Needs

An Approximate Solution

Since the procedure just described is

quite lengthy and quite expensive to execute

on a computer, an approximation was used

to compute the heat loss in the analysis of

integrated systems conducted for this study.

The approximation was simply to use equation A-29 or equation A-31, depending on

whether the system was modeled with a

fixed-outlet temperature T O or with a fixedflow rate fr This equation was used with an

empirically derived value for UL which wa s

assumed to be constant throughout th e

year. Measured values of UL for a variety of

different collector designs are shown in

table VII I-A-IO.

Table VIII-A-IO compares the monthly

output of collectors calculated assuming a

U-value independent of temperature with

the collector output calculated using the

variable U-value procedure of the previous

sect ion. Computatio n of the variabl e

U L

-values using the iterative solution included all corrections discussed in th e

previous section: it assumed F R = 0.95, it

used Duffie’s assumptions about radiative

sky temperatures, and it assumed typical

values for heat loss through the back and

sides of collectors. The comparisons al l

assume a constant flow rate of 10 cm3

/se c

per square meter of collector area A C and a

fixed inlet temperature for collectors in

Omaha. The “average” U-value used for the

fixed U-value case was computed using the

annual average daytime temperature and

wind velocity.

It can be seen from table VII I-A-IO tha t

the total annual output agrees to within

about 0.5 percent in all four cases run. The

monthly totals vary by as much as 10 percent, but for the two-cover, selective absorber case which has thermal losses comparable to the tubular flat-plate collector

generally modeled, the monthly differences

are always less than 3 percent. During the

winter, the fixed U-value approach gives

less output than the variable U-value approach. This indicates that lower ambient

temperatures during the winter decrease the

U-value more than the increase due to higher wind velocities, even for single cover collectors.

The fixed U-value approach reduced the

cost of computer computation by about 50

percent.
Chapter IX

ENERGY CONVERSION WITH

HEAT ENGINES

Chapter IX.— ENERGY CONVERSION WITH HEAT ENGINES

Page

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329

Thermodynamics. . . . . . . . . . . . . . . . . . . . . .. 330

Cogeneration. . . .......................332

The RankineCycle. . ....................333

Cycle Performance . ..................336

Turbine Efficiency . . . . . . ..............338

PerformanceWith Heat Recovery. . . . ...340

PerformanceWith Backup PowerSources343

State of the Art. . . ....................345

System Costs... . ....................352

Costs of Organic RankineSystems. .. ...354

The BraytonCycle. . ....................354

System Efficiency. . ..................360

OperationWith Fossil Backup. .........365

System Costs... . ....................365

TheStirlingand Ericsson Cycles.. . .......366

Priniciples of Operation . ..............366

Design Alternatives. . . . . ..............368

Performance . . . . . . . . . . ...............376

PerformanceWithWaste Heat. .........378

SystemCosts. . . . ....................379

State of the Art. . ....................381

Other Heat-Engine Designs . .............383

The Thermionic Converter . ............383

ThermoelectricConversion . ...........385

The Nitinol Engine. . ..................385

Osmotic-Pressure Engine. . ............386

EnvironmentalandSafetyProblems. . .......387

Fluorocarbons . . . . . . . ..................387

Page

Noise . . . . . . . . . . . ......................388

WaterUse in SteamCycles . .............389

Sodium and Potassium Vapor . ...........389

LIST OF TABLES

Table

No. Page

I. Organic Power-CycleWorking Fluids

Used in SystemTesting or in

Development . . . . . . ...................339

2. Efficiency of Steam Rankine Devices

Operated From Storage at Reduced

Temperature . . . . . .. ...................345

3. Ratio of EnergyRequired for Boiling

to Total EnergySenttoTurbine . .........345

4. Small Steam RankineTurbines . .........346

5. Design and Performance Parameters of

Current and Projected RankineAutomotive

PowerSystems . ......................347

6. ExperimentalOrganic RankineTurbines

in the UnitedStates. . ..................348

7. Brayton Cycle Efficiencies. . ............363

8. Stirling Engine Characteristics . .........378

9. Performance of Free-Piston Stirling

Engine Designs of EnergyResearch and

Generation, inc.. . .....................379

10. Performance of SunPower Free-Piston

Devices . . . . . . . . ......................379
LIST OF FIGURES

Figure No, Page

1. Cycle Efficiencies of Heat Engines . . . . . .. 331

2. System Performance (Ratio of Electric

and Thermal Energy Produced to Energy

Entering the System). . . ................333

3. Rankine-Cycle Devices With Heat

Extraction . . . . . . . .....................335

4. Temperature Dependence of RankineCycle Devices . .......................337

5. Rankine-Cycle Expander Efficiencies. ....338

6. Efficiency of Backpressure Steam

RankineDevices . .....................340

7. Schematic Diagram of the SolarTotal

Energy System lnstalled at Sandia

Laboratories in Aibuquerque, N.Mex. ....341

8. Electric and Thermal Performance of a

12.5 MWe Generai Electric Extraction

Turbine . . . . . . . . . . ....................342

9. Designs for Providing Backup Power

for Solar Rankine-CycleSystems . .......344

10.TheSunstrand 100kW Organic Rankine

Turbine . . . . . . . . . .....................348

11. Components of the Solar Heated, RankineCycle Electric Power/3-Ton Air-Conditioning

System . . . . . . . . . .....................349

12. Flow Diagram of the Soiar Heated,

Rankine-Cycle Electric Power/3-Ton

Air-ConditioningSystem . ..............350

13. United Technologies Design for

Rankine CycleAir-Conditioner . .........351

14. Sun PowerSystemsFlow Diagram for

5HP, Rankine CycleAir-Conditioner. .. ...352

15. Experimental Expander at General

Electric . . . . . . . . . .....................353

16. installed Costs of Steam Rankine

Turbines . . . . . . . . .....................354

17. installed Costs of Organic Rankine

Turbines . . . . . . . . .....................355

18. installed Costs of Field-Erected

Boilers . .............................356

19. Four Brayton-CycleSystems Compatible

With SolarApplications . ...............357

20. Components of a 500kW GasTurbine. ....358

Figure No. Page

21. 50 MWe Closed-CycleGas Turbine .......359

22. Section Through a Combined Gasand

SteamTurbine Powerplant. . ............361

23. Artists’sRendering of Proposed SolarHeatedAirTurbineGenerating Facility ...362

24. Temperature Dependence of Optimum

Cycle Efficiencies. . ...................363

25. The Effect of Waste-Heat Extraction

on the Performance of Gas Turbines . . . . . . 364

26. Closed Regenerated-Cycle GasTurbine. ..364

27. installed Costs of Open-Cycie

BraytonTurbines. . ....................365

28. ldealStirlingand Ericsson Cycles.. .. ....367

29. Calculated Performance of a 225-HP

Stiriing Engine as a Function of the

Specific PowerandWorking Gas . .......369

30. Phiiips Rhombic-DriveStirling Engine ....37O

31. Swashplate Stirling Engine . ............371

32. Calculated Performance of a Philips

Rhombic-DriveStirling Engine . . . . . . . . . . .371

33. Free-PistonStirlingand Ericsson

Cycle Designs.. . .....................372

34. SunpowerSystems Free-Piston Stirling

and Ericsson Cycle Design Approach. ....374

35. Free-PistonTotal EnergySystem . .......375

36. Free-PistonTotal EnergySystem . .......376

37. The Philips Design for a Stiriing

EngineTotal EnergySystem . ...........377

38. Heat Balance for the Stirling and

Diesel Engine... . .....................379

39. ElectricandThermal Output of a

Stirling Engine.. . .....................380

40. Weight-to-PowerRatios of EnginesWith

lnternal Combustion and of Stirl`ing

Engines . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .381

41. Cost of Diesel Engines . . . . . . . . .........381

42. 200-Watt,SunpowerStirling Engine,

Mounted in ConcentratingCollector .. ...383

43. identification of Thermionic

ConverterComponents . ...............384

44. Effect of ColiectorTemperature

on Thermionic Efficiency . ..............385

45. The Nitinol Engine. . ...................386
Chapter IX

Energy Conversion With Heat Engines

BACKGROUND

The basic resource of solar energy is a constant temperature thermal

source at approximately 10,000° F.* If this resource is to be used for

anything other than lighting, the energy received must be converted into a

more useful form. This paper examines three separate technologies for accomplishing this conversion:

1. Thermal devices which use sunlight to heat a fluid and direct this

heated fluid either directly for applications requiring heat (such as

space-heating or industrial processes) or to operate heat engines;

2. Photovoltaic devices which convert light directly into electricity; and

3. Photochemical devices which use light directly to drive chemical

react ions.

This chapter compares the costs and performance of a number of specific

heat-engine devices. Photovoltaic and photochemical processes are discussed in chapter X.

A large number of devices for converting thermal energy into mechanical

energy and electricity have been developed over the years, and many of these

could be converted for use with solar power. The only energy conversion

cycles with which direct solar power would not be easily compatible are

those requiring internal combustion— diesel engines, for example, would be

cliff i cult to convert to a direct-solar application.

The following cycles are considered in

some detail:

Rankine-cycle systems using organic working

fluids such as Freon show the greatest promise for producing useful mechanical work

from solar-heated fluids with temperatures

in the range of 650 to 3700 C (1490 to 6980

F). The technology is reasonably well-developed and prototype devices are currently

available in sizes ranging from kilowatts to

many megawatts. An Israeli manufacturer

has been selling small units for nearly a

decade, and devices are now available from

U.S. manufacturers. Small organic Rankine

devices are similar to air-conditioners working in reverse and should be able to exhibit

the reliability, simplicity, and low cost enjoyed by refrigeration equipment. Organic

Rankine devices are able to make efficient

use of the temperatures available, but the

*This is the effective “blackbody” radiation temperature of the Sun, not its actual surface tempera

ture

Ji,{. , $J ( ) - 2’2

overall cycle efficiency is relatively low (5 to

20 percent) because of the low theoretical

maximum efficiency of low-temperatur e

heat engines, Low-temperature engines can,

however, be operated from fluids produced

by simple nontracking collectors and tracking collectors with low-concentration ratios

and can use relatively inexpensive storage.

Steam Rankine devices are probably the

most attractive contemporary heat-engine

designs for temperatures in the range of

3700 to 550“C (6980 to 1,0220 F). (Reciprocating steam engines and saturated steam

devices can also operate at lower temperatures. ) A variety of devices are available and

the technology is mature, although the market for small steam turbines has, unti l

recently, been quite small and designs are

somewhat outdated. Rankine-cycle devices

operating with steam or other working fIuids

at temperatures higher than 600“C (1,1100 F)

are possible, but the equipment must be

made from special materials.

329
330 ● So/ar Technology to Today’s Energy Needs

One difficuIty with Rankine devices operating in conventional temperature regimes is

that their generating efficiency falls sharply

if waste heat is recovered.

Brayton-cycle (gas-turbine) engines operate

at temperatures of 900“C (1 ,6520 F). Commercial devices are available in a variety of

sizes, although efficient devices are typically only available in units producing more

than 1 MW. The technology is well understood, although work is needed to develop

reliable heat exchangers for solar receivers

and regenerators needed to improve efficiency. The efficiency of Brayton-cycl e

devices is lower than steam Rankine efficiencies, even though the former operates

with much higher initial temperatures. The

high temperature of the exhaust, however,

permits recovery of waste heat without excessive loss of generating efficiency.

Stirling-cycle piston devices are available

on a prototype basis and can operate at temperatures in the range of 6500 to 800°C

(1 ,2000 to 1,4700 F). Development work is

needed to design a reliable commercial device. The engines will probably initially be

best suited for applications where individual

devices generate less than about 300 kilowatts. They may be able to achieve very

high efficiences (40 to 50 percent).

Advanced Ericsson free-piston engines and

highly regenerated Brayton devices with

multiple stages of reheat are being investigated, and some units are in the development stage, Those cycles would operate in a

temperature range of 7500 to 1,000“C

(1,382 0 to 1,8320 F) and also show promise

of achieving high efficiency. The free-piston

device may be able to achieve high efficiency with a small, relatively simple engine.

Research is also underway on several

other advanced concepts including: Rankine-cycle devices operating with liqui d

metals, therm ionic devices (prototypes of

these devices are available which operate in

temperatures of 1,0000 to 1,500 “C; efficiency is poor, but they reject heat at temperatures high enough to drive other engines in

a bottoming cycle), and thermoelectri c

sol id-electrolyte devices (systems have been

tested which operate in the temperature

range of 7500 to 1,5000 F, but research is in

a very early stage).

The overall system efficiency of these

cycles is illustrated in figure IX-I. The temperature ranges which can be produced by

different types of collectors are also shown

to indicate which collectors would be used

to provide heat for the cycles.

THERMODYNAMICS

The cost of most solar systems depends

critically on the cost of the collector field

and the area of collectors required will depend directly on the efficiency of the energy

conversion system employed. The efficiency

of an ideal heat engine increases with the

temperature available. If heat is available at

a constant temperature Th and is rejected at

a constant temperature T C

, the maximum

engine efficiency is given by the Carnot effi-

(1)

(Both temperatures must be expressed as absolute temperatures. ) I n many cases, however, heat will be available only in the form

of a heated fIuid which cools as energy is extracted. If energy is extracted from a fluid

which cools from Th to T' h

, while giving up

heat to the engine, in this case, the max-
Ch. IX Energy Conversion With Heat Engines ● 331

Figure IX-1 .—Cycle Efficiencies of Heat Engines

10

* Local temperatures In the combustion chamber only Exhaust gas IS 9000 to 1,4000 F

Note References for Indlvidual estimates can be found In relevant sections of this chapter

SOURCE Prepared by OTA using manufacturer’s data

the collector system and for engine components. Materials have been developed

which can be used with gas turbines at

temperatures in the range of 1,8000 F, and it

may be possible to develop material (such as

silicon nitride or silicon carbide) which can

be used at temperatures as high as 2,0000 to

2,5000 F in the next decade. ’ The cost of

systems using such materials has not yet

‘Arthur L Robinson, “Making Gas Turbines From

Brittle Materials, ” Science, Vol. 188 (1975), p 40

been established, however, and could be

quite high.

In spite of the theoretical increase of efficiency with temperature, there are a number

of reasons to believe that the use of the

highest available temperature may not result in either the most inexpensive solar

energy or even the highest efficiency. If

both the cost and the efficiency of collectors or of storage devices increases rapidly

with temperature, for example, there would

be an optimum temperature which would
332 ● Solar Technology to Today’s Energy Needs

minimize overalI system costs. (The preceding chapter has presented evidence that collector costs may be nearly independent of

the temperatures produced, but this result

can only be tested with more experience.)

Even if collector and storage costs are independent of temperature, however it may

not be desirable to operate at the highest

available temperature because the efficiency of real devices does not necessarily increase with increasing temperature. It can

be seen from figure IX-I, for example, that

the efficiency of steam turbines operating at

8000 to 1,0000 F can be higher than the efficiency of gas turbines operating at 1,4000 to

1,8000 F. A final choice of designs will require a net assessment of the economic attractiveness of the integrated system.

COGENERATION

The analysis of efficiency becomes significantly more complex when there is a need

both for electricity and thermal energy .

There are several alternatives to choose

f rem:

●

●

●

The

Generate electricity at the maximum

possible efficiency and produce the

thermal energy with a separate collector or with a fossil boiler;

Generate electricity at the maximum

possible efficiency and use a hea t

pump to produce the needed thermal

energy (i. e., the heat engine would reject heat at the lowest temperature); or

Use a heat engine which rejects heat at

a temperature high enough to be useful

for the thermal processes (cogeneration).

optimum selection will depend critically on the nature of the thermal and electric loads and on the details of the operational performance of available hea t

engines.

If ideal systems were available, the second alternative would always define the

maximum efficiency; the cogeneration system could equal the maximum efficiency

only if the load had a unique ratio between

thermal and electrical requirements defined

by the waste-heat temperature. With other

ratios, some part of the load would have to

be met either with a backup “boiler” or with

a heat engine using the highest possible

electric-generating efficiency.

The complexity of the situation can be

een in figure IX-2. This figure shows how the

energy required by several types of systems

varies as a function of the ratio between

electric and thermal demands. The most efficient system is the device employing an efficient heat pump and an efficient hea t

engine. Commercial heat pumps are not

able to produce temperatures above 100 “C,

but most space-conditioning applications

and many industrial processes can use heat

at temperatures below 100°C. The seasonal

coefficient of performance of space-conditioning heat pumps is typically below 2,

however, and figure IX-2 shows that with this

efficiency, cogeneration systems using engines with lower electric-generating efficiency could have better overall performance

than high-efficiency engines driving heat

pumps as long as the ratio of electric to thermal demand is below about 0.8. The leastefficient system shown, however, is the relatively low-efficiency engine with a backup

boiler for providing thermal energy.

All that can be concluded from this analysis is that great care must be taken in

designing systems to maximize efficiency.

The decision depends heavily on the ratio

between electric and thermal loads and the

way in which this ratio varies over time. If

electricity which exceeds local requirements

can be sold to a utility, the perspective of a

designer could change. Since the ratio between thermal and electric loads could be

changed, in this way the overall efficiency

of the system would always be reduced by

increasing the electric to thermal ratio. In

some circumstances, the greater value of

the electricity generated would compensate

for the extra cost. The addition of storage

equipment could also permit some adjustment of the ratio between the thermal and

electric demands placed on the energy conversion system.
Ch. IX Energy Conversion With Heat Engines ● 333

14

12

1,0

0.8

0 6

0 4

0 2

0

Figure lX-2.—System Performance (Ratio of Electric and Thermal Energy Produced

to Energy Entering the System)

Steam rankine with NO extraction

ExtractIon steam Ranklne

(steam at 300°F)

Gas turbine with waste heat boiler

— – — (steam at 300°F )

————. Combined cycle (COP as shown)

Backup ‘boiler’ assumed 100% efficient

0.45

0.33

o 0.25 0.50 0.75 1.00 1.25

All thermal demand Ratio of electric energy delivered All electric demand I

to thermal energy delivered

Note. It is possible for a heat pump to perform several units of useful work for each unit of energy consumed since the “energy consumed” by the engine

does not count the energy In the ambient alr used as a source of heat “pumped” by the device

SOURCE. Prepared by OTA using manufacturer’s data

The following review of each cycle in- THE RANKINE CYCLE

eludes a brief description of the way the cycle works, an analysis of the prospects for

using the cycle for cogeneration, an esti- The Rankine cycle has been used since

mate of the cost and performance of dif - the early 19th century for everything from

ferent design options, and a summary of the steamboats to nuclear powerplants. It concurrent status of research, development, tinues to be the most commonly used for

and manufacturing. generating stationary power. Designs have,
334 ● Solar Technology to Today’s Energy Needs

of course, improved over the years and a

variety of devices are currently available.

Typical Rankine cycles operate as follows: a liquid is pumped under pressure into

a boiler (which could be a receiver in a solar

collector) where heat is added, boiling the

liquid into a vapor (in some applications the

vapor is also superheated); the vapor is then

expanded over turbine blades or in a piston

to produce mechanical energy; the low-pressure vapor which emerges from this expansion process is condensed to a liquid and

pumped under pressure to the boiler where

the cycle begins again. In sophisticated

systems, efficiency can be increased 4 to 5

percent by preheating the water returning to

the boiler with hot vapor extracted from

high-temperature stages of the expansion

process. Water is the fluid most commonly

used in the cycle, but other liquids can offer

advantages at lower temperatures.

There is no fundamental limit to the temperatures which can be used in the Rankine

cycle, but practical limits are imposed b}

the steel alloys used in boilers and other

components. The highest practical temperature with current technology is about 1,1000

F. Higher temperatures may be possible in

the future using advanced materials, but a

recent study by the Federal Power Commission concluded, “It would probably require

10 to 15 years to develop materials for use at

temperatures above 1,2000°F.” 2 It may be

possible to achieve much higher operating

temperatures if liquid metals are used as a

working fIuid.

Two techniques are used to extract heat

from Rankine-cycle devices for direct thermal applications. Figure IX-3A shows a simple “backpressure” device in which lowpressure vapor is simply sent directly to the

process loads. If organic fluids are em -

ployed, or if the process requiring thermal

energy could contaminate the water used in

‘John H. Nassikas, Chairman, Advisory Committee

Report: Energy Conservation, Federal Power Commission, The National Power Survey, December 1974, p

86.

the turbine, a heat exchanger is used which

condenses the turbine fluid and transfers

energy to a separate piping system used in

spaceheating or industrial processes. The

temperature of the steam produced is controlled by the pressure maintained at the

end of the final turbine-expansion stage.

This temperature can be changed somewhat

to adjust to different loads, but a large

amount of control is not possible. The system is most useful in situations where there

is a relatively constant demand for process

heat during the year; it does not require

costly condensing equipment or coolin g

towers since this operation is being performed by the industrial process or building

heaters. If there are periods when the heat is

not required, however, condensing stages

must be purchased to reject the unwanted

heat. The backpressure devices producing

steam at high pressure can significantly

reduce the amount of electricity generated

by a given rate of steam flow. A very large

fraction of the total energy sent to the system can be recovered as steam heat or electricity, however, since the only losses in the

system result from mechanical losses in the

turbine, losses in the generator, and oilcooler losses. These losses are quite small.

An alternative approach is illustrated in

figure IX-3B. This system, called “extraction” turbine (or “pass out” turbine by the

English and Europeans) is simply an ordinary

condensing Rankine device with provision

for extracting steam at some intermediate

stage in the turbine-expansion process. The

device has the advantage of permittin g

great flexibility in the temperature and

quantity of steam produced but, of course,

it requires the purchase of condensers, cooling towers, and relatively expensive lowpressure expansion stages. (Low-pressure

stages are physically large since the volume

of the steam has increased at the lower

pressure, and thus these stages are more

costly per unit output.)

Steam turbines are used in many industrial cogeneration installations, but are used

by less than 1 percent of the “total energy”

space-conditioning instalIations in the
Ch. IX Energy Conversion With Heat Engines • 335

Figure lX-3.— Rankine-Cycle Devices With Heat Extraction

Boiler

Boiler

Pump

Generator

SOURCE Prepared by OTA using manufacturer’s data
336 ● So/ar Technology to Today’s Energy Needs

United States.

3 This is due to the fact that

their efficiency is low when there is a small

demand for space heat, and that local ordinances frequently require experienced

operators to be on duty whenever pressurized steam is used. Extraction turbines are,

however, frequently used in district heating

systems in Europe where a variety of designs

are employed. Stal-Laval apparently has a

system which saves the expense of a condenser by using low-temperature steam to

provide “heating of swimming pools, snow

melting in winter, pavement heating, etc.” 4

One difficulty with all large steam turbines is that all of these devices require

complex procedures when they are started

and when they are turned off. Usually an

hour or more is needed and skilled personnel must be present. The process is expensive and wastes energy. It could be a serious

barrier to the use of these devices in solar

applications where systems must be turned

on and off each day. The problem could be

alleviated if fossil fuel were used to fire the

system when storage was exhausted.

Cycle Performance

The Rankine cycle permits a great range

of design options and the system efficiencies vary widely. Efficiency depends principally on the following design features:

●

●

●

●

The maximum temperature and th e

condensing temperature of the cycle.

The working fIuid used.

The efficiency of the turbine (or piston)

expansion process and the mechanical

efficiency of the system.

A number of features, such as th e

number of stages of expansion used,

the use of feedwater heating, etc.

~1 971 Total Energy Directory and Data Book,

Volume 1, Total Energy Publishing Company, January

1971, pp. 40-66,

4!. G. C. Dryden, editor, The Efficient Use of Energy,

IPC Science and Technology Press, Surrey, 1975, p.

355.

The overall system efficiencies of a variety of simple and regenerated Rankine-cycle

devices (i.e., systems in which the working

fluid is preheated by hot sections of the turbine before being sent to the boiler) are illustrated in figure IX-4. The extremely high

efficiencies of large contemporary steam

plants result from the use of many reheat

cycles (i.e., adding heat to the working fluid

at some stage during expansion) and extremely high pressures. Such sophistication

cannot be afforded in small systems. The attractiveness of organic working fluids depends on the power levels required and the

characteristics of available heat sources.

Organics may prove to be more attractive

than steam in small systems working at relatively low temperatures, although idea l

steam cycles can produce competitive efficiencies. There are several reasons for this:

●

●

●

The organi c working fluids remai n

vaporized under temperature and pressure conditions where steam would be

gin to condense. In steam systems, the

turbine blades can be eroded severely

by the impact of droplets on the rapidly

moving blades. These droplets reduce

system reliability and system life, as

well as efficiency. This problem can be

reduced if the turbine is divided into

several stages with liquid removed between stages, but this adds to the system’s costs

The efficiency of the organic turbines

proves to be greater than steam turbine

efficiencies in many systems now operating at low-power levels (figure IX-5).

The optimum turbine speed of organic

systems is lower than equivalent steam

systems (potentially saving costs).

Organic systems are relatively simple

compared to multiple-stage steam de-

‘Dean T. Morgan and Jerry P. Davis (Thermo Electron Corporation), High Efficiency Decentralized Electrical Power Generation Utilizing Diesel Engines Coupled With Organic Working Fluid RankineCycle

Engines Operating orI Diese/-Reject Steam, NSF Grant

No. G 1-40774, November 1974, pp. 8-28.
Ch. IX Energy Converison With Heat Engines . 337

Figure lX-4.—Temperature Dependence of Rankine-Cycle Devices

Maximum Cycle Temperature (°F)

SOURCES Low-Temperature organic and steam efflclencles computed by R E Barber “Solar powered Ranklne CYcle Engine Cycles —Character!stlcs and

Costs, ” June 1976, with the followlng assumptions” Expander efficiency 80 Percent, PumP efflclencY 50 Percent, Mechanical eff Iclency 95 Percent, Condensing

temperature 95° ● F, Regeneration efficiency 80 percent, High side pressure loss 5 percent, Low side pressure loss 8 percent

“High-temperature steam efflclencles from National Power Survey Adwsofy Panel Report On Energy Conservahon, December 1974, page 102

vices and can be constructed inexpensively from low-cost materials if a noncorrosive working fluid is used. The systems thus have the potential for lon g

life and high reliability at relatively low

cost.

Thermodynamic properties can be optimized by selection of an appropriat e

organic working fluid for maximum efficiency and power; up to 35 percent greate r

power output can be achieved with organic

relative to steam, depending on heat-source

temperature characteristics.

The advantages of organics are counterbalanced to some extent by the fact that

many of the fluids being studied are toxic or
338 . Solar Technology to Today’s Energy Needs

Figure lX-5.—Rankine-Cycle Expander Efficiencies

efficiency

# l o

6

1 10 100 1000 10000

Engine Size (kW)

Reciprocating steam

Steam turbine

organic turbine

Reciprocating organic turbine

SOURCE. Prepared by OTA using manufacturer’s data

flammable. The systems are sealed, however, and only small amounts of the fluid

should leak from the cycle in a properly

maintained system. Another potential drawback is the cost of the fluids, although fluid

costs tend to be only a small fraction of

overall system costs even if expensive fluids

are used. (Water clearly has the advantage

of being cheap, plentiful, and nontoxic. ) The

characteristics of a variety of materials

which have been considered for turbine applications are shown in table IX-I.

Refrigerants are attractive for applications up to about 4000 F. They are nontoxic

and the technology of Rankine systems using these materials is very well known since

refrigerators are simply Rankine cycle s

operating in reverse. A number of other

materials have been examined for application at temperatures up to about 8000 F, and

the search for the desirable materials is continuing. In the temperature range of 7000 to

1,1000 F, there is no advantage in using

fIuids other than water.

Many early organic systems have had reliability problems resulting from failures of

bearings and seals. These problems have apparently been overcome by several manufacturers, and high reliability is one of the

selling points of organic Rankine engines designed for use in isolated regions. Reliable

systems are presently quite expensive ,

however.

Turbine Efficiency

Turbine performance is limited by the size

of the equipment as welI as by the temperatures available. Figure IX-6 illustrates the

efficiency with which turbines of varying
Ch. IX Energy Conversion With Heat Engines ● 339

Table IX-1. —Organic Power-Cycle Working Fluids Used in System Testing or in Development

Maximum

boiler

out let System Current

temperature Freezing test development

Fluid Developers ‘F point ‘F experience Flammablllty underway Comments

Freon 11

Freon 114

Freon 22

Isobutane

Thiophene

FC-75

(3 M Co )

Chlorobenzenes

IHI (Japan) -250

-400

425

-500

550

-600

-600

-600

-137

-256

-217

-37

-76

625-650 -82

-700 75

SOURCE Thermoelectron Corp
340 ● Solar Technology to Today’s Energy Needs

Figure lX-6.— Efficiency of Backpressure Steam Rankine Devices

sizes can extract the energy available in the

fluids sent to them. It can be seen that with

current designs the efficiencies of small systems are quite low. This is in part the necessary result of the fact that a clearance must

be maintained between the turbine blades

(or pistons) and their containment cylinders.

(This is not a limiting factor for single-stage

impulse turbines. ) The fluid which can leak

through this aperture does not perform work

and thus limits efficiency. In smaller systems, the clearance area is a larger fraction

of the total useful turbine blade area and

thus smaller systems are more seriously affected by these effects. The figure illustrates, however, that several advanced

turbine and reciprocating engine designs

have been able to achieve relatively high efficiencies even at small sizes.

High turbine efficiencies have been demonstrated even in very small devices. BarberNichols Engineering Company, for example,

has constructed a 2.5 hp turbine, operating

on a refrigerant, which demonstrated a turbine efficiency of 72 percent. 6 A small multivane expander developed by the General

Electric Co. has demonstrated efficiencies

as high as 85 percent. 7 It is clear, therefore,

that high-turbine performance is not necessarily restricted to large devices.

Performance With Heat Recovery

The decline in generating efficienc y

which is experienced by steam Rankine devices operating with backpressure and ex-

‘Robert E. Barber, “Solar Air-Conditioning Systems

Using Rankine Power CycleDesign and Test Results

of Prototype Three-Ton Units, ” Proceedings, the Second Workshop on the Use of Solar Energy for the

Cooling of Buildings, Los Angeles, Calif , Aug. 4-6,

1976, p. 91.

7S. E. Eckard and J. A. Bond, “Performance Characteristics of a Three-Ton Rankine Powered Vapor Compression Air-Conditioner, ” Proceedings, the Second

Workshop on the Use of Solar Energy for the Cooling

of Buildings, op. cit., p. 110.
Ch. IX Energy Conversion With Heat Engines “ 341

<

F’

l’: I I . l-:=

-l-’ 1+ 1/ “’ .’- ““fh L “’.”~— — -k : A I “ I I

c.-

. .

I

,-:= ..—

-!

,

,-

-UMAL -’

TJm I J

I

I

rl

II

II

II

IL

I

I

I

:

I

I

I

I

I

;

I

I

I

I

I

I

I

I

1

I

iI

I

I

I

I

I

I

; w

I I

,

,

I

. II — . —.. —.. -
342 Ž Solar Technology to Today’s Energy Needs

traction systems is shown in figures IX-7 and

IX-8. The efficiencies shown in these figures

represent a highly simplified analysis of the

cycle and are intended only to illustrate the

sensitivity of generatin g efficiency t o

changes in several important variables .

Figure IX-6, for example, illustrates the difficulty of using backpressure turbines with

relatively low-inlet temperature systems to

produce process steam at high pressures and

temperatures. Generating efficiency falls

off rapidly with increasing backpressure and

Figure lX-8.— Electric and Therma Performance of a 12.5 MWe

General Electric Extraction Turbine
Ch. IX Energy Conversion With Heat Engines Ž 343

the problem is exaggerated unless highturbine efficiencies can be achieved.

Figure IX-7 illustrates the operation of a

backpressure device using toluene as a

working flu id which has been installed in

Albuquerque to test the concept of solarpowered “total energy” systems. The system

is equipped with a cooling tower since the

heat extracted from the turbine is used for a

heating and cooling application where loads

are Iikely to vary greatly from day to day.

The performance of an extraction device

is illustrated in figure IX-8, using a format

which has become standard for presenting

data about such systems.

Steam Rankine devices have been selected by all three contractors working on a

design for DOE’S 10 MWe solar centralreceiver demonstration plants, 8 9 10 The total

energy test design developed by Sandia uses

the toluene-based Rankine cycle shown in

figure IX-7.

Performance With Backup Power Sources

It is possible to design Rankine-cycle systems which are capable of operating both

from fossil fuels and from solar power. The

temperatures used are low enough to permit

piping energy from boilers operated from

different sources to a single Rankine turbine

device. In addition, the boilers can be externally fired so coal or other solid fuels can be

easiIy used for backup fuel.

Two approaches are shown in figure IX9A. The most efficient type of backup systems provide energy from a fossil-fire d

boiler or a storage unit at temperatures and

pressures which are as close as possible to

those of fluids supplied directly from the

‘Quarterly Report No 1, Central Receiver Solar

Thermal Power System, Phase 1, january 1976, Martin

Marietta (ERDA Contract E(04-3}1 110)

‘Central Receiver Solar Thermal Power System,

Phase 1, Final Report, January 1976, McDonnellDouglas Astronautics Company (ERDA Contract

E(04-3-1 108)

‘“Solar Pilot Plant, Phase 1, Conceptual Design

Report, Dec. 18, 1975, Honeywell, Inc. (ERDA Contract E(04-3}1 109)

solar colIectors. With this approach, the performance of the cycle is not changed by a

shift from solar to backup power.

If a storage device capable of supplying

temperatures close to those supplied directly from the solar collectors is not available

at an acceptable price, it would be possible

to use a turbine with two different inlets:

one for high-temperature fluids received

directly from the collectors, and one for

lower temperature fluids received from storage. (This is shown by the dotted line in

figure IX-9 A.) Steam turbines with multiple

inlets have been avaiIable for many years,

although most are relatively large.

Another approach which may be attractive under some circumstances would use

the “hybrid” system illustrated in figure IX9B. In this design, solar energy at relatively

low temperatures is used to boil the working

fluid and a fossil boiler is used to superheat

the liquid to the turbine inlet conditions,

This system takes advantage of the fact that

the majority of the energy absorbed by conventional Rankine cycles is absorbed at a

constant temperature while the liquid is

converted into vapor. This system would

take advantage of the relative simplicity of

solar collectors operating at moderate temperatures, while permitting more efficient

utilization of the high-flame temperatures

available from burning fossil fuels.

The performance of these different approaches can be summarized in the following simplified analysis. If the fraction of the

thermal energy applied to the system which

leaves as mechanical energy through the

high-pressure and low-pressure stages of the

mixture emerging from the high-pressure

stage is available to be sent to the lowpressure stage (the remainder being used to

preheat the feedwater going to the boiler),

the total electric output of the engine E is

written as follows:

(3)

Here Qb is the energy available from the
344 • Solar Technology to Today’s Energy Needs

Figure lX-9.— Designs for Providing Backup Power for Solar Rankine-Cycle Systems

A. Direct fossil backup

Fossil

+

boiler 300° F/60 psia

rq

-- To process loads

~ -1,

,

Solar

collec

950°F/1 250 psi /

\?: , p:ak~—’

Hp ;

tor

mc

“~ ~ ~ 600°F/350 psia

2 P

v

2

v I 1

L–- -

Con-

~~.1

denser

-- --– ~ From process loads

Deaerator

Pump ———— Storage discharge flow if

storage can discharge at 950° F

B. Fossil boiler used for superheating

~—---

● To process loads

L-’-”l

Generator

Solar M .

collec- — ●

tor

M. (l~f) ?

denser

[

I &

Pump

d!

L

Deaerator

M. = mass flow

4

from boile r

From process

loads

SOURCE. Prepared by OTA using manufacturer’s data
Ch. IX Energy Conversion With Heat Engines ● 345

fraction of the energy available from the

first turbine stage which is sent to the secavailable for process loads. Using the same

notation, the energy available in the process

heat Q P can be written as follows:

(4)

the temperature of the process heat stream.

These parameters are illustrated in figure IX9B. A sample set of these parameters is illustrated in table IX-2 for a turbine operating with 9500° F, 1,250 psia steam. The

decrease in system performance resulting

from the lower storage temperatures can be

clearly seen. The performance can be improved considerably if the fossil boiler is

used to raise the temperature to the original

inlet conditions.

Table IX-2. —Efficiency of Steam

Rankine Devices operated From Storage

at Reduced Temperature

Single-feed water No feed water

regenerator regenerator

Assumptions: generator efficiency = 95%

turbine efficiency = 800/0

pump efficiencies = 700/o

steam extracted for reheat at 300° F

inlet conditions 950° F/l 250 psia

fraction of energy entering system which

leaves as mechanical power in the first turbine

stage

fraction of energy entering system which

leaves as mechanical power in the second

turbine stage

300° F energy available for process heat or low

pressure turbines per unit of energy available

from the high-pressure turbine

SOURCE Prepared by OTA using manufacturer’s data.

The performance of designs using a fossil

system to superheat the steam can be estimated from the efficiencies shown in table

IX-2 and the ratios shown in table IX-3. This

last table indicates the percentage of the

energy entering the turbine which results

from the boiling process. Boiling can represent a large fraction of the total energy requirements. The boiling temperature for this

system shown is 5720 F. Using fossil fuels

only to provide superheat would effectively

increase the efficiency of converting fossil

energy into electric output.

Table IX-3 .—Ratio of Energy Required for

Boiling to Total Energy Sent to Turbine

Boiling

temper- Ratio

ature

extraction turbine 950° F/l 250 psia

(feedwater regeneration) . . . . . . . . . . 572° F 0.76

950° F/1250 psia(no feedwaterheat) 572° F 0.79

600° F/350 psia backpressure50 psia 486° F 0.91

400° F/150 psia backpressure50 psia 247° F 0.99

SOURCE: Prepared by OTA using manufacturer’s data.

State of the Art

While Rankine-cycle engines are available in a variety of sizes, most of the development work in the United States in recent

years has been directed to perfecting very

large devices optimized for centralized utility applications. Because of the limited demand for small steam turbines, designs tend

to be somewhat antique, although interest

in smaller devices has been greatly increased in recent years.

A number of companies are working on

devices capable of improving the performance and reducing the costs of smal l

Rankine-cycle systems. Table IX-4 indicates

some of the steam turbines which were identified by Sandia Laboratories in their review

of devices for use in their total energy system. Extraction turbines and backpressure
346 • Solar Technology to Today’s Energy Needs

Table IX-4.—Small Steam Rankine Turbines

(1973 Dollars)

Capacity cost Source

(kW) ($ in thousands)

2

3

5

10

20

100

250

400

500

1000

2.0

4.5

3.7

3.0

4.1

3.8

2.5

6.0

18.0

11.3

10.0

9.6

9.0

50.0

17.5

30.0

100.0

70.0

45.0

5

2

1

1

1

5

5

1

1

1

5

6

2

3

1

4

2

3

4

SOURCE: Solar Total Energy Program Semiannual Report, April

1975- September 1975, Sandia Laboratories, Solar Energy

Projects Division, April 1976, p. 96.

Source Legend:

1 - Coppus Engineering Corporation

2- The Terry Steam Turbine Company

3- The Trane Company, Murray Division

4- Turbodyne Corporation, Worthington Turbine Division

5- The O’Brien Machinery Company

6- Carling Turbine Blower Company

turbines are also available in the sizes of interest to intermediate total energy applications. Most interest in this research comes

from several directions including:

1. A desire to develop devices to improve

the fuel economy of diesel-generator

sets and gas turbines through the use of

a “combined-cycle” approach.

2. Making use of waste heat from other industrial processes which is available at

temperatures of 2500 to 1,0000 F.

3. Interest in exploiting geothermal energy in the range of 2000 to 6000 F.

4. Interest in developing new engines for

automobiIes and other vehicles.

The Environmental Protection Agenc y

and the State of California funded research

on steam-powered automobiles, beginning

in 1972, which Ied to the construction of two

prototype steam vehicles–one built b y

Steam Power Systems and the other by Aerojet Liquid Rocket Company. There has also

been a considerable amount of interest and

investment in this area by private companies, including Lear, Carter Enterprises,

and Saab-Scandia of Sweden. Table IX-5

summarizes the performance of some of the

equipment which has been investigated.

Interest in small, combined-cycle systems

has come mostly from companies which

construct onsite generating facilities for

remote locations (pipeline pumping sta -

tions, offshore drilling rigs, etc.). international Harvester, Solar Division, for example, believes that a steam turbine which

operates on the heat exhaust from their 2.6

MWe “Centaur” gas turbines could produce

an additional 1.3 MWe, resulting in increasing generating efficiency from 26.6 percent

to over 40 percent. Similarly, a steam turbine which operates on the heat exhaust

from their 7 MWe “Mars” unit, could produce an additional 3.3 MWe, resulting in increasing generating efficiency from 31.5 to

43.5 percent. The Thermo Electron Corp.

and several other companies are working on

small steam turbines for similar applications .

1 2

In addition to development work on improved steam cycles, a considerable amount

of attention is being directed to the development of organic Rankine cycles. Work in this

area has also been stimulated primarily by a

desire to develop high-efficiency, combinedcycle, generating systems. Geothermal and

even space applications have also motivated research in organic cycles. Several

large organic Rankine units are now in use in

various parts of the world. DOE is supporting work in organic Rankine devices of intermediate sizes by the Sunstrand Corporation,

Thermo-Electron Corporation, and Mechanical Technologies, Inc. A summary of the

‘ ‘jet Propulsion Laboratory, An Autornobi/e Power

Systems Evaluation, August 1975, p. 7-2.

‘

z Donald L. Kearns, Regional Manager, Government Relations, International Harvester, Solar Division, letter dated Mar. 10, 1977.
650

1000

IL-4

Series-P

Variable

135

Variable

2500

IL-4

spool

Variable

49

Variable

2400

v-4’

HAP

Variable

184

Variable

1800

IL-2

PAP

Fixed

30

12: 1

6000

IL-4

Series-P

Variable

68

Variable

3200

IL-4

HAP

Variable

50

Variable

2000

246

33

228

20

244

27

210

35

193

10

228

20

212

32

71

85

68

N/D

N/D

N/D

75

87

75

N/D

N/D

N/D

N/D

N/D

N/D

75

87

75

150

755

0.77

65

N/D

1.03

145

N/D

0.79

90

N/D

0.55

90

600

0.67

60

N/D

0.79

765 857 835 338 520 N ID

characteristics of some of the devices which

have been tested can be found in table IX-6.

The Sunstrand Corporation work started

in 1961, and a number of units rated from

1.5 kilowatts up to 600 kilowatts have been

operated successfully. One of the Sunstrand

100-kilowatt units has been modified t o

operate on 5500 F solar heat and has been

tested at the Sandia Albuquerque Labs.

Development work at Thermo-Electron

has been proceeding in several different

areas. Among the organic Rankine cycle

systems (ORCS) applications are a 10 MW

combined steam/ORCS unit, a 4.3 MW

diesel/ORCS unit, a 1.25 MW ORCS bottoming unit, a 400-kilowatt ORCS as a prime

mover, and a 40-kilowatt ORCS bottoming

unit for a truck diesel engine. 3 The turbines

used by Thermo-Electron are typically axial

impulse turbines and may have up to six

stages. These designs all utilize eithe r

Fluorinol 50 or Fluorinol 85.

No large organic system is now being

manufactured on a large scale, although a

number of prototype units have been successfully operated. Engines ranging in size

from a few kilowatts to a few megawatts are

commercially available from Sunstrand, S u n

Power, Kinetics Corporation, and othe r

firms, although none is produced in large

‘

] Organ/c Rartkine Cycle System tor Power Generation from Low-Temperature Heat Sources, Thermoelectron Corporation, Sept. 10,1973.
348 • Solar Technology to Today’s Energy Needs

quantities. (A 100 kW Sundstrand unit is

shown in figure IX-10. ) The Ormat Corporation of Israel has sold a number of small

organic Rankine-cycle devices for use where

extremely high reliability is required (e. g.,

remote pipeline pumping stations). The high

reliability guarantee results in a high initial

cost. Several hundred of these units have

been sold over the last 10 years and millions

of hours of operating experience have been

obtained.

Table lX-6.– Experimental Organic Rankine Turbines in the United States

Sunstrand Elliot ● Thermo- Thermo- ThermoAviation Turbo- Electron Electron Electron

machinery

Working

fluid . . . . . . Toluene

Turbine Inlet 550° F

Turbine type Singlestage

partial

admission

impulse

turbine

Unit-rated 36 kWe

capacity

Fluorinol- Fluorinol- FluorinolIsobutane 8 5 50 85

350° F 550° F 600° F 550° F

3-stage Single- 3-stage 1-stage

double stage axial axial

flow axial axial flow turbine turbine

turbine impulse

turbine

65 MWe 104 kWe 33 kW shaft 3 kWe

● Developed for geothermal application.

SOURCE: Prepared bv OTA using manufacturer’s data,

Figure IX-10.— The Sunstrand 100 kW Organic Rankine Turbine

SOURCE: Sunstrand Aviation, Rockford, Ill., “100 kW Organic Rankine Cycle Total Energy System.”
Ch. IX Energy Conversion With Heat Engines ● 349

A number of firms are also developing these engines is demonstrating acceptable

organic Rankine devices which could be lifetimes and reliabilities. A critical element

used for small residential or commercial in- in this design work is finding an inexpensive

stallations. Several of the designs now under safe working fluid with an acceptably long

consideration are illustrated in figures IX-II life. A variety of other design details (blade

through IX-I 5. Hundreds of hours of oper- shapes, etc. ) will undoubtedly also be imating experience have been achieved with proved for optimum performance. The techmany of these devices, even when the units nology of steam turbines has been develare unattended; the expanders have run very oped over nearly a century. While organic

quietly and without vibration. (The sound is systems can profit from this development

similar to the hum of an air-conditioner. ) work, much remains to be done to realize

The major development problem fo r their full potential.

Figure IX-1 1 .—Components of the Solar Heated, Rankine-Cycle Electric Power/3-Ton

Air-Conditioning System

Prototy~ Integratd System

The Organic Turbine

SOURCE Robert E Barber, “Solar Air Cmd!tlon!ng Systems Using Rank!ne Power Cycles —Des@n and Test Results of a Prototype Three Ton Unit, ” PrO.

ceedlngs 01 the Second Workshop on fhe Use of Solar Energy for the Coo/lng of Bulkftngs, Los Angeles, Calif., Aug 461975, PP 101 and 102
350 Ž Solar Technology to Today’s Energy Needs

Figure IX-12.— Flow Diagram of the Solar Heated, Rankine-Cycle Electric power/3-Ton

Air-Conditioning System

T = 215° F SOLAR T = 205° F

T

WATER WATER

m—[ RANKINE CYCLE REFRIGERANT 113

1—1 AIR CONDITIONER REFRIGERANT 12 DESIGNED AND FABRICATED BY

SOLAR COLLECTOR WATER BARBER-NICHOLS ENG CO

r J COOLING WATER DENVER, COLORADO

SOURCE: See figure IX-1 1.
Ch. IX Energy Conversion With Heat Engines ● 351

Figure lX-13.— United Technologies Design for Rankine Cycle Air-Conditioner

BASELINE DESIGN CONDITIONS

FLUID R 11

COOLING = 37 TONS

COP = O 36

COLLECTOH STORAGE

SIMULATOR

+ -1

T = 213CF

VAPOR

d

II GEN “

L_dL . . . . . J

STEAM T = 203° F

EXP VALVE

T = 20Qo F

— —b

k

TURBINE /

r

I N = 28,560

RPM

T = 137’F I

T = 159° F

I

H20

FREON

I

PUMP

8 - - I T = 105° F

COMPRESSOR

3--------

T = 45°F

- –--—

POWER LOOP COOLING LOOP

SOURCE” Fran Blancardl and Maurice Meader (Un[ted Awcraft Research Laboratories), “Demonstrat~on of a 3-Ton Rankine Cycle-Powered Air-Cond/t~oner, ”

F’roceed)ngs of the Second WorksfIop on ftre Use of So/ar energy for the Coollng of Bul/dings, Los Angeles, Cal If., Aug. 4-6, 1975, p. 142.

Thermostat Electrlc Motor

{v>. Y

I Multl.Vane

, u

Alr

L[qu[d

I Separator Expander I

t ftt

1

compressor T (

I

Hot Water I Press ;

LooP ‘

I

Control I

L J

Recetver

1

)-i

H20

(COOLING LOAD)

b

EVAPORATOR

/

i

EXP VALVE

T = 105’F

H

Refrigerant Loop

Water

Coollng Loop

SOURCE S E Eckard and J A Bond (General Electrlc Company), ‘“Performance Characterlstlcs of a 3-Ton Ranklne Powered Vapor.Compression Air.

Condltloner,” Proceedings of Ihe Second Workshop on the Use of So/ar energy for the Coo/ing of f3ul/dmgs, Los Angeles, Callf , Aug. 4-6, 1975 p 129
352 • Solar Technology to Today’s Energy Needs

Figure lX-14.— Sun Power Systems Flow Diagram for 5 HP, Rankine Cycle Air-Conditioner

solar

collector

n n

EXPANDER

u

R-1 14 180° 141 pSl 1 20” 33 psl \

/ \ \ I water 80°

165° 185° POWER OUTPUT

Freon

/ ‘0’’ ”

condenser

water \I

pump

\ //\

\ [ (3

1

U water pump

Freon 80° Ilquld

pump ~

(

FOR FIVE NET HORSEPOWER

\

I

R-1 14 2.86 GPH

Hot water 14 GPH

Cool water 28 GPH I

water

cooling ~

grid

m

SOURCE: Sun Power Systems, Inc , Sarasota, Fla.

While improvements in design will certainly be forthcoming, there is no apparent

technical barrier to developing a commercial device. The General EIectric device,

based on a multivane expander, is an adaptation of a system called “ELEC-PAC” which

was designed to be a simple, portable, total

energy system used to provide electricity

and heat for mobile homes, boats, or recreational vehicles. The device is shown in figure

IX-I 5, together with some of the advantages

of the device claimed by G. E.

It can be seen from the pictures in figure

IX-11, that devices large enough to provide

adequate power to a single-famiIy home can

be quite small. The entire device shown is

not much larger than the air-conditioner

which it would be designed to replace.

System Costs

The costs of Rankine-cycle devices i n

small sizes is difficult to estimate, as relatively few installations are presently being

constructed; however, the cost of installing

contemporary steam devices in the megawatt range can be estimated with fair accuracy. The costs can be divided into four

general categories:

1. The cost of heat exchangers which may

be required to transfer heat from the

collector circuit or storage device to

the working flu id in the turbine;

2. The cost of the turbine itself;

3. The cost of any condensing systems

and cooling towers which are employed; and
Ch. IX Energy Conversion With Heat Engines ● 353

Figure lX-15.– Experimental Expander at General Electric

FEATURES AND CHARACTERISTICS OF

MULTI VANE EXPANDER

High Brake Efflclency Over a Wide Range of

— Load(ng

— Speed

— Vapor Pressure

Tr)lerates Wide Range of Vapor Quallty

— No Eros[on Problems

— Nc) LIq utd Compression Problems

H g h Tcirque a! Zero Speed

— Self Startlnq Under Load

Low Speed Compared to Turbine

— Matches May Load Requirements

Stmplr3 Construct Ion

— Nr, Valves or Gears

— Simple Seals and Con/e~tlonal Bearings

PII~m IIs Slm~le Control System

— Lc A N o se and VI brat 10 r

– Gc,(,d LI fe Potenllal

INLET

PI

P2

SOURCE Eckard and Bond, op cIt , page 123
354 Ž Solar Technology to Today’s Energy Needs

4. The cost of a backup boiler to provide

energy when solar energy is not available.

It would be possible to reduce the cost of

the smaller turbine units if large numbers

are manufactured. The Jet Propulsion Laboratory estimated the costs of producing

units in the 150-kilowatt size range i f

manufacturing were performed on the scale

with which automotive engines are now produced. There estimates show a wholesale

price of $13/kW and a retail price o f

$17/kW.14 This is more than an order of

magnitude lower than the cost of the units

manufactured with conventional turbin e

manufacturing techniques.

The cost of condensing units and cooling

towers required by condensing systems (in

addition to the turbine costs shown in figure

IX-16) are illustrated in figure IX-17. Costs

range from about $90/kWe to abou t

$30/kWe.

The cost of providing backup power to an

onsite solar system is shown in figure IX-18.

The costs assume the construction of field-

“An Automobile Power S ysterns Evaluation, Jet Propulsion Laboratory, Volume 11, pp. 11-12.

Figure lX-16.– Installed Costs of

Steam Rankine Turbines

\

{~

o.nlbum hx @loV wc4wrw8umtulblrH Iiulda

cod bolw w

Cmdmm!aw Wbhn

COndemm MfbhO

mlcmduwwJ tuli4bu

{1a403 p@@

10 N 30 40

.l.w!rlCO. !put MWe

T.rtlne COSIS (ncl.deI“stallallo” .. ”!,01s ..6 0..”,.1., c.o,ler coats ,.,1.0. suloiwr

rem. ”.l wale< $re”lme”l !“elstrx~e .sh rerro”al bul!d W, PIPI!W !“slr. me.!, O“. !

w.,*.“OSt Wk, ”X<lllaVq ”lPm.”t

,+ , ,.s.. .!,. m.!rm L P!.. ! ,1.’!!1 “!w.r . ,,*

erected boilers and include the cost of maintaining all of the ancillary equipmen t

(pumps, feedwater treatment, etc.) required

for the operation of the system. Approximately 10 percent of the cost shown is due

to devices designed to remove sulphur and

particulate from the boiler exhaust, and

about 10 percent is traceable to systems for

fuel-handling and storage.

Costs of Organic Rankine Systems

Estimating the potential cost of organic

Rankine devices requires a considerable

amount of speculation, since the few units

now on the market are essentially handmade. I n spite of this, there is a fair degree

of agreement about the price of devices

manufactured in relatively small numbers.

This pattern could change, however, if massproduction techniques were employed for

the smaller units. The figure shows estimates

indicating that production of 10,000 t o

20,000 units per year could reduce the costs

of units in the 5 to 10 kWe range to $200 to

$300/kW, a price which compares favorably

with the costs of even the larger steam- turbine systems. These costs are in general

agreement with the costs of commercially

available reciprocating and centrifugal airconditioning systems. The comparison is a

reasonable one for determining the potential future price of mass-produced organic

Rankine turbines since the mass-produced

air-conditioners employ a nearly identical

technology.

THE BRAYTON CYCLE

The Brayton cycle (which uses gas at all

phases in the thermodynamic cycle) has

been used extensively for jet aircraft and is

commonly used by utilities to provid e

power during peak demands. Its usefulness

for peaking applications results from the

low initial cost of the devices. Since they are

relatively inefficient, however, they are

typically used only to help meet peak loads

and are typically used by utilities less than

1,000 hours per year.

The rising cost of liquid and gaseous fuels

compatible with conventiona l Brayton-
Ch. IX Energy Conversion With Heat Engines ● 355

1000 —

8’00 —

600 —

400 —

200 —

Figure IX-17.— Installed Costs of Organic Rankine Turbines

/-”

20,000 unltslyear

\

‘----

‘--@ / Notmcl.cfing —o

I

installation

r l -

10 100 1000

System Size In Kilowatts

10,000

SOURCE

A

B

c

D

E

F

G

Milton Van Horn (Market Manager General Electrlc Advanced energy grou P Private communlcatlon, June 1, 1976) (estimates In 1975 dollars)

Price of electrlc chll Iers (assume 17°. cycle efflc Iency when operated as turbine generators)

Beno S!ernllcht (Mechanical Technology Inc ) Power, June 1975 p 71

Sun Power Systems Inc (Dr M{nto. President, prlvafe communication April 19, 1976)

R E Barber “Solar Powered Organic Ranklne Cycle Engines Charactenst!cs and Costs “ June 1976

Thermo Electron “ H Iah Efflc lenc~ Electrc Power Generation”, November 1974, paqes 59 and 510 (Increased by 9°. for lnflatlon since 1974)

Sun Po-wer Systems ~rlce estlmaie 1.21175 (200° F (n let)

cycle gas turbines has dramatically in -

creased operating expenses. There is, however, technology which shows promise of

permitting Brayton-cycle devices to operate

from external heat sources, such as coal

(burned in a fluidized-bed boiler or a similar

device) or from solar sources. The major barrier to the use of these devices has been the

development of heat exchangers which are

capable of transmitting high temperatures

into gaseous working fluids. Such materials

now exist, but further work is needed to develop commercial devices. The Boeing Corporation has recently completed a successful test which subjected the receiver to

thermal-cycling equivalent to 30 years of

operational performance. A heat exchanger,

constructed from a material called Haynes

188, survived 10,560 cycles with a high temperature of 1,5000 F. Tests will also be done

on a device using an Inconel 617 heat exchanger. 5 These materials will, however, be

quite expensive.

As was the case with the Rankine-cycle

devices, the maximum temperatures available for use with Brayton-cyc!e devices is

limited by the performance of inexpensive

“John P Gintz, Program Manager, Boeing Company Engineering and Construction Division, C/osedCyc/e, l-ligh- Temperature Centra/ Receiver Concept for

Solar Electric Power, E PRI, February 1976.
356 ● Solar Technology to Today’s Energy Needs

Figure lX-18.— Installed Costs of Field-Erected Boilers*

1-

30

20

10

\

\

\

\

\

\

1250psig 900°F

———— 650 psig 750°F

\

\ %

\

\

--

+

-- ‘ - c oa I

-

-

—-—

-

-

-

-\_

- -

‘ - o i l

‘ - -

--— —- ——— ——— o i l ——

I I I I I I I

100 2 0 0 300 4 0 0 5 0 0 6 0 0 7 0 0

Millions of Btu/hour

● Includes coal handling, ash removal, fuel storage, sulphur removal, and electrostatic precipitator for particulate

removal, boiler erection, foundation, buildings, instruments, auxillary equipment, ductwork and stack, electric

material in boiler building, feedwater sampling and treatment, fuel and ash handling, and indirect distribution

costs.

SOURCE Thermo-Electron Corp A study of Inplant Electrlc Power Generation of the Chemical, Petroleum Reflnlng, and Paper and Pulp Industries, June

1976, pages 317 and 319

materials. Temperatures of 1,5000 F are typical for Brayton devices. Temperatures as

high as 1,8000 F can be used, but this significantly shortens the expected operating life

of the units.

The Brayton cycle has an advantage over

Rankine-cycle devices when used in connection with a total energy or cogeneration

system because the Brayton devices operate

at much higher initial temperatures. This

means that heat can be recovered from the

exhaust gases without reducing generating

efficiency to the extent that Rankine-cycle

efficiencies are reduced.

Four different Brayton-cycle system s

which may be of interest for solar energy applications are shown in figure IX-I 9. The simple cycle is the basis for most of the gasturbine power generated in the Unite d

States. Commercial devices are available
Ch. IX Energy Conversion With Heat Engines Ž 357

Figure IX-19.— Four Brayton-Cycle

(A) SIMPLE CYCLE

r *

A~r Inlet -1 r-l solar collector

and/or fossil burner l - l

Systems Compatible With Solar Applications

r‘Xhaus’”r waste.heat boiler

I 1 J

generator

Compressor \

1 -@

Turbine

(B) REGENERATED CYCLE

air inlet

regenerator

compressor \

(c)

(D)

CLOSED CYCLE Turbine 7

generator ~

1

fess burner or

INVERTED

I I regenerator

waste heat

CYCLE

generator

\ \

EzEl “

Alr waste heat

Inlet bo{ler

SOURCE Prepared by OTA using manufacturer’s data

J

~ Exhaust
358 ● So/ar Technology to Today’s Energy Needs

which range in size from a few kWe to over

50 MWe. 16

Ambient air is compressed, heated, and

expanded through a turbine. About twothirds of the turbine’s power is required to

provide the compressor with power, with the

remaining power being available for operating a generator. The gas is heated in a conventional device by igniting oil or natural

gas in a combustion chamber. In a solar or

an externally fired device this combustion

chamber would be replaced with a high-temperature heat exchanger. A commercia l

‘K. Samuels and J. T. Meador, M/US Technology

fva/uation: Prime Movers, Oak Ridge National Laboratory (OR NL-HUD/MIUS-l 1 ), April 1974, p. 22.

single-cycle gas turbine is shown in figure

IX-20.

A variety of techniques can be used to improve the efficiency of the cycle. The air can

be cooled during the compression stage, for

example, and the gas can be reheated during

expansion in the turbine. The most effective

technique for increasing efficiency, however, is to use the techniques in connection

with a regenerator as shown in figure IX19(B). In this design, the compressed air is

preheated by the turbine exhaust before being heated in the combustion chamber or

heat exchanger. Cycle efficiencies can be increased from 28 percent to nearly 38 per -

cent in this way. The major barrier to the use

of such devices, however, is the cost and

reliability of the regenerative heat ex -

changers.

Figure lX-20.— Components of a 500kW Gas Turbine

‘URNER —————cl

L

I 7X

STARTER DOG ~,rrt ,,.=n ‘f

ACCESSORY [JA

DRI

)4 GEARBOX ‘, “ . .

e ) ‘1 L/ ‘

,4

MAIN GEARBOX —

)+&Ls\:&’’,~A,z-~Hous,;TuRB’NEENTRyvOL”TE

l“

OIL DRUM COMPRESS~R STATOR

CASING

SOURCE. Electrical Research Assoclatlon, Llmlted “Electrlc Power Plant Intmatmal 1975-1976 edition” Surrey, England, 1975

(Acknowledgements to Centrax LTD)
Ch. IX Energy Converison With Heat Engines ● 359

Commercial regenerative heaters can be

guaranteed only if they are not turned onand-off frequently, since the materials used

fail if they are repeatedly heated an d

cooled. This I imitation is, of course, inconsistent with using the devices for meeting intermittent loads in utility peaking a pplications, and it is inconsistent with the

demands of a solar installation where the

available energy is intermittent. Progress in

developing reliable regenerators is being

made, however, and the Garrett Corporation

claims to have a device which is capable of

withstanding large numbers of on-and-off

cycIes without damage. 1

7

A third approach to the Brayton cycle is

to close the cycle as shown in figure IX19(C). In this device, the gas emerging from

the turbine is sent back to the compressor

instead of being exhausted. The device must

be fired externally since the circuit must be

closed. The closed cycle has a number of advantages, the most important of which is

that it permits the use of gases other than

air. Helium and other light gases can be

1‘Patrick G Stone, Garrett Corporation, private

communication, December 1975

used to improve heat-exchange characteristics. The closed cycle can also be used at

higher pressures with the advantage that

smaller turbines can be used. No penalty

need be paid in efficiency for using gases

other than air. 1

819

While a few closed-cycle, gas-turbin e

devices have been built in the United States

(a closed-cycle device developed for NASA

by the Garrett Corporation has been operating or under test for about 15 years),

several German and Swiss firms have had

devices operating from coal for a number of

years. The cycle is being investigated for use

with gas-cooled nuclear reactors. A picture

of a large, closed-cycle plant now being

checked out in Oberhausen, Germany, is

shown in figure IX-21. A closed-cycle gasturbine system is being investigated by EPRI

for a central receiver solar application .20

The “inverted” Brayton cycle illustrated

in figure IX-19(D) may offer some advantages when used as a bottoming cycle for

‘

8 Samuels, op. cit , p. 42

‘9R, M. E, Diamant, Total Energy, pergamon Press,

pp. 229-232

20G intz, op. cit.

Figure IX-21 .—50 MWe Closed-Cycle Gas Turbine

HELIUM TURBINE INSTALLATION

AT OBERHAUSEN, GERMANY

T INTER- 1

COOLER

LOW- HIGH. HIGH- LOWPRESSURE PRESSURE PRESSURE PRESSURE

COMPRESSOR COMPRESSOR TURBINE TURBINE

*

\

GENERATOR

b

HEATER ~ ,1

(RECEIVER)

h

v

RECUPERATOR

PRECOOLER

i

HELIUM CYCLE SCHEMATIC

SOURCE Glntz, John R (Boe}ng Company, Englneerlng and Construction Dlvlsion), “Closed Cycle High Temperature Central Receiver Concept for Solar

Electrlc Power, ” February 1976, EPRI
360 ● Solar Technology to Today’s Energy Needs

any process generating hot air at ambient

pressures. 21 It may also have some advantages in small solar applications. The device

operates by heating ambient air in a heat exchanger before the gas is sent to the turbine.

The hot air expands through the turbine into

a vacuum produced by a compressor (which

acts like a pump in this application), which

exhausts the gas at ambient pressure in an

open-cycle system or returns it to the heat

source in a closed-cycle system. The efficiency of the inverted cycles can be as high

as similar devices operating at higher pressures. The advantage of such a device for

solar applications is that the heat exchanger

can operate at atmospheric pressure. This

greatly reduces the demands placed on the

materials which transfer high temperatures

to the engine. The major disadvantage of

this approach is that the density of the gas is

much lower than in a pressurized system

and thus the turbine units must be relatively

large. This is less of a restriction in small

sizes, however, since small turbines must be

relatively larger per-unit-energy output to

minimize the effect of gas escaping around

the ends of the turbine blades. Another

disadvantage of the inverted cycle is that a

heat-rejection heat exchanger is required in

addition to the heat exchanger where external heat is applied. This is not a problem in

applications where a second heat exchanger

is required for a heat-recovery system. Heat

exchangers will need to be relatively large,

however, because of the low density of the

gases used in the cycle.

Few inverted-cycle devices have been

constructed, but a prototype, developed by

the Garrett Corporation for a gas-fired heat

pump, has operated successfully sinc e

November 1976. The designers claim that an

efficiency of over 38 percent has bee n

measured on this device in initial tests .22

“D, C. Wilson, and N. R. Dunteman, The Inverted

Brayton Cycle for WasteHeat Utilization, ASM E

publication, 73 CT-90, April 1973,

~Zpatrlck C, Stone, Garrett Corporation, Private

communication, December 1976.

Another approach which can be used to

increase the generating efficiency of Brayton-cycle devices is to recover the energy in

the turbine exhaust in a boiler and use the

heated fluids generated in this way to drive

a steam or gas turbine. Overall efficiencies

as high as 48 percent in large units can be

achieved in this way. 23

Waste heat can be recovered from gas

turbines in two ways. The most commonly

used technique is simply to install a large

boiler in the path of the turbine exhaust.

Heat can also be extracted between compression stages if more than one compressor

is used. One system for removing thermal

energy from a Brayton-cycle device is shown

in figure IX-22.

Two approaches have been proposed for

using Brayton-cycle turbines in solar applications. Small units could be mounted at

the focus of individual tracking-collectors,

or they could be located at the counterweight position of these collectors with heat

transferred to the units through a heat pipe.

Heat pipes using sodium vapor have been

developed which operate successfully in the

temperature regimes necessary.

In a central receiver used for large r

systems, it would be possible to pipe the hot

gases to a heat exchanger on top of a

receiver tower. This is the approach being

examined by EPRI (figure IX-23).

System Efficiency

The optimum cycle efficiencies of simple

and regenerative Brayton cycles are shown

in figure IX-24 as a function of the temperature available. (It is important to recognize,

however, that the comparison is made only

for turbines operating at full load; operating

efficiencies at part load may compare quite

differently.) The great advantage of developing materials capable of operating at high

temperatures can clearly be seen. The performance of actual units is summarized in

table IX-7. It can be seen that the efficiency

2’Morgan, op. cit., pp,4-9.
Ch. IX Energy Conversion With Heat Engines ● 361

Figure IX-22.—Section Through a Combined Gas and Steam Turbine Powerplant

1 Gas turbine package

2 Load gear

3 Generator

4 Steam turbine

5 Crossover pipe to adjacent condenser

6 Waste heat boiler

7 Exhaust gas silencer

8 Stack

9 Inlet silencer

10 Air intake building with filter

7

t

II r,I i 1111 ‘r- ”-n 111~

+1--ul~ --- K.= — – - —

- “ ‘[ g; -

‘

 - - ●

1 2 3

.

SOURCE Electrical Research Assoclatlon Llmlted, E/ecfrfc Power Plant IfJternafloflal, 1975-1976 edltlon, Surrey, England, 1975 (With acknowledgements

to A E G Kanfs )

, . 4 ,,. !1
362 ● Solar Technology to Today’s Energy Needs
Ch. IX Energy Conversion With Heat Engines ● 363

of simple-cycle devices decreases dramatically in small sizes. The 2.7 MW “Centaur ”

Figure IX-24.—Temperature Dependence

of Optimum Cycle Efficiencies

gas turbine manufactured by International

Harvester, for example, can achieve 26.6-

percent efficiency, while the small 20 k W

Gemini unit achieves only 13.7 percent efficiency. The inefficiency of smaller engines

is decreased somewhat if regenerators are

40

30

20

10

used. A small turbine developed for auto -

mobile applications, for example, can develop 26.8-percent efficiency and, as noted

earlier, the small inverted-cycle turbine developed by the Carrett Corporation has

shown 38-percent efficiencies in preliminary

tests. All of these efficiencies are, however,

substantially less than the 47-percent effi0

500 1000 1500 2000

ciency which apparently can be” achieved by

the 50 MWe closed-cycle device.

Turbine inlet temperature, ‘F

The generating efficiency of a gas turbine SOURCE. Beno Stemlicht, “The Equipment Stale of LowLevel Heat

Recovery,” Power, June 1975, page 73

I

is reduced if waste heat is recovered in a

Table IX-7 .—Brayton Cycle Efficiencies

Cycle Cycle Efficiency’

Nominal

Size (kW)

Present

(1976)

Future

1980-85 Reference

(1)

(1) (2)

(1)

(1)

(1)

(5)

(2)

(3)

(8)

(4)

(9)

(8)

(8)

(8)

(8)

(8)

(8)

(lo)

Simple cycle 20

100

800

2700

7200

13.7

13.7

22.8

26.6

22-28

31.5

38

32-35

Regenerated cycle 20

100

central station

2800

26.8

35

32.2

25-32

35-39

Closed cycle

(Regenerated)

Combined cycle 4200

(Simple cycle) 4550

57400

36.8

40.2

44.4

40.7

43.6

48.0

47.0

Combined CYCIe 3606

(Regenerated gas turbine) 3860

73700

235000

*Losses in the mechanical equipment WiII reduce the cycle efficlency by 3-8%

sOURCE (1)

(7)

(8)

(9)

(lo)
364 ● Solar Technology to Today’s Energy Needs

boiler placed at the turbine outlet. Overall

performance of the simple-cycle gas turbines producing both thermal and electric

energy is shown in figure IX-25. It can be

seen that, in contrast with the Rankine cycle, the efficiency changes very sIightly as a

function of the temperature of the waste

heat recovered.

The regenerative cycles apparently exhibit a combined electrical and thermal efficiency similar to that of the simple-cycle efficiencies shown in figure IX-25, but the ratio

between electric and thermal output in -

creases as a resuIt of the regeneration.

The performance of a closed-cycle Brayton-cycle system, which provides thermal

energy to a district heating system requiring

pressurized water at temperatures between

2000 and 3000 F and returns the water at

1220 F, is illustrated in figure IX-26. In this

case, it can be seen that the combined efficiency can exceed 80 percent.

in a solar application where alternating

current is required, all of the efficiencies

Figure lX-25.—The Effect of Waste-Heat

Extraction on the Performance of Gas Turbines

90

80

70

[

Combined electric and

‘————— thermalefficiency

60

t

I

50 1-

1– Thermal efficiency

40

Electric efficiency

30 -

20

t

Electric efficiency = (electric output)/(energy

entering turbine)

10

t

Thermal efficiency = (energy in steam)/(energy

()~

entering turbine)

100 200 300 400

Steam pressure (psig)

SOURCE Calculations based on performance of Rolls Royce RB.211

Gas Turbine (28,960 BHP), 2°10 electrlc efftclency loss due to

backpressure

Figure lX-26.— Closed Regenerated-Cycle Gas

t

Turbin~

.

.

.

I 1 1

200 300

Pressurized water temperature “F

(water return temperature = 1229F

SOURCE. Dlamanl, et al , op CII , page 244

discussed above must be reduced by the efficiency of some type of power-conditioning

equipment. This is because the speed of

Brayton-cycle devices changes rapidly as a

function of the incident power; thus, frequency control cannot be maintained in an

alternator, although the Brayton-cycl e

device can be locked into a utility grid frequency if it is attached to utility power. In

such cases, electric output power will be

proportional to the energy available from

the solar collector.

This frequency control problem can be

solved for a stand-alone system by rectifying

the output of the alternator and then using

an inverter to produce a constant 60-cycle

output. The efficiency of this process will be

typically in the range of 85 to 90 percent.

Constant-speed mechanical devices are also

available which can produce a constant

speed in an output shaft, given variable

speed inputs. It is, for example, possible to

operate a drive-flywheel combination and

controller in reverse. There have also been
Ch. IX Energy Conversion With Heat Engines ● 365

ingenious proposals for providing frequency

stability by continuously changing th e

number of fixed magnets in the alternator.

All of these schemes result in some loss of

efficiency.

Operation With

It should be

Fossil Backup

possible to design a Brayton

cycle system which is capable of operating

from either fossil or solar energy sources. In

a closed cycle, all that would be required

would be to insert an additional heatexchanger and fossil burner into the piping

circuit. In an open-cycle turbine, a fuel injector could be included in the circuit for

use when backup was needed. There might

be some difficulty in operating a fossilburning device which was attached to the

focus of a tracking collector because the exhaust might accelerate the aging of optical

components; however, this problem should

not be insurmountable.

System Costs

The installed costs of gas turbines of

various sizes are illustrated in figure IX-27.

There is a clear economy of scale in these

devices, given current manufacturing techniques, although the effect is not as pronounced as it was in the case of Rankinecycle engines. The enormous advantage of

using mass-production techniques for the

production of small equipment is also apparent from this figure.

The total cost of an installed Brayton

device must include the cost of several components in addition to the turbine. Waste

heat boilers (if used) would add $15 to $75

per kilowatt to the costs shown in figure

IX-27 (depending on the temperature and

pressure of the process steam required). z

’

Miscellaneous equipment for controls and

24 Sternllcht, op. clt

Figure lX-27.— Installed Costs of Open-Cycle Brayton Turbines

\

Saturn ~’--’<”~

Centaur J

 -

- ‘----

Mars *

100 –

r

I

10 50 100

● Under development

Estimated cost of mass-produced

regenerated engine (JPL Automobile Assessment, pages 11, 12)

..1. __ L.. _ . ___ . . . . . . . .1.

500 1,000 5,000

SOURCE Pr~ces based on estimates made by International Hame5ter for unl!s shown Re9enerafor Prices are assumed to be 20°. of the turbine price

(see Stern llcht, op clt p 72)
366 ● So/ar Technology to Today’s Energy Needs

other equipment will add about 20 percen t

to the cost.2 5 The cost of the equipment required to maintain a constant output frequency will vary with the size of the installation. The cost of power-conditioning equipment is discussed in detail in the section on

electric storage. If a backup fossil capability

is required for the equipment, fuel storage

would add approximately $30 per kilowatt. 26

THE STIRLING AND ERICSSON CYCLES

Even if devices employing Rankine or

Brayton cycles wer e constructed fro m

perfect components (i.e., if there were no

friction or fluid losses around turbin e

blades), these devices would not achieve the

efficiencies of ideal heat engines operating

between the same temperature limits. This is

because neither cycle accepts heat only at

the highest cycle temperature nor rejects

heat only at the lowest temperature; an

ideal engine would maintain a constant temperature during these heat-exchange processes.

Both the Stirling and the Ericsson cycles

maintain a constant temperature during the

heat-exchange processes associated with expansion and compression and thus are, in

principle at least, capable of achieving the

maximum permitted Carnot efficiency. Existing engines which approximate Stirling

and Ericsson cycles are externally fired,

piston engines. (No real device actually

maintains a constant temperature during

heat addition or heat rejection and thus the

devices fail to operate on a true Stirling or

Ericsson cycle.) In addition to the potential

for high efficiency, they should also be

capable of long lifetimes, and quiet, reliable

operation.

Also, since heat is applied externally, the

engines are easily compatible with solar

energy applications, and backup energy can

be provided from any type of fuel. In total

energy applications, they have the addijsEstimate made for OTA by the Ralph parsons

Company,

26 Sukuja, et al,, Op. cit., PP3-26

tional advantage of rejecting nearly all of

their waste heat in the form of heated liquids, and thus a heat-recovery boiler is not

required. The cycles are capable of operating at a variety of different temperatures,

with the upper-temperature range limited

only by the capabilities of the heat-ex -

change materials. They also have an inherently low RPM and thus need not use expensive gear-reduction systems. Devices based

on the Ericsson cycle also can be designed

to operate at relatively low inlet temperatures and can span the entire spectrum of

temperatures available from solar collectors. The systems are particularly interesting

for onsite-power applications since efficiency is not sacrificed by building units as small

as a few kilowatts.

There have been proposals for using Stirling engines for vehicle propulsion, electricpower generation (including residential ,

total-energy systems), artificial hearts, and

water-pumping applications.27 28 29 30 31 32 A

major study conducted recently by the jet

Propulsion Laboratory concluded that the

Stirling engine was one of the two most

promising systems for future automobile

engines because of its potential for high efficiency, low emissions, and quiet operation. 33

Principles of Operation

The operation of ideal Stirling- and Ericsson-cycle devices is explained in some detail

in figure IX-28. Both cycles described here

“W, R. Martini, Developments in Stirling Engines,

presented to the American Society of Mechanical

Engineers, New York, N. Y., Nov. 26-30, 1972

‘

8 Stir/ing Tota/ Energy System (a Philips Corporation

paper).

Z9W. R, Martini, IJnCmventjOm I Stir/lng Engines fo r

the Artificia/ Heart Application, Proceedings, 9th lntersociety Energy Conversion Engineering Conference, San Francisco, Calif , Aug 26-30,1974.

‘OG. M Benson, “Thermal Oscillators, ” Proceedings, Eighth Intersoclety Energy Conversion Engineering Conference, Philadelphia, Pa., August 1973.

313-5k W Stir/ing Engine Alternator, ERG, Inc., report

to u.s Army, MERDC (1969).

32 Stir/ing Engine Driven Tota/ Energy System, ERG ,

Inc , report to Am Gas Association (1969).

“An Automobile Power Systems Evaluation, jet Propulsion Laboratory.
Ch. IX Energy Conversion With Heat Engines ● 367

I I I

0m 0ml

Id

H

I I I ($?E

lid] J

uolsld 6U!yJOM
368 ● Solar Technology to Today’s Energy Needs

would be capable of ideal efficiency. Both

cycles absorb and reject heat at a constant

temperature and employ a permeable thermal mass, called a regenerator, to heat and

cool the working fluid without exchanging

energy with systems external to the engine.

This regenerator is the key to the system’s

efficiency. In principle, it cools heate d

working fluids passing through it, absorbing

energy from the fluid in the process, and

restores all of this energy to the fluid when

cool fluid passes through it in the opposite

direction. The only difference between the

two cycles is that in the Stirling cycle the regenerative heating and cooling of the working fluid occurs in a constant volume while

the Ericsson cycle performs this function at

a constant pressure.

It was noted earlier that the efficiency of

Brayton-cycle devices could be improved

with regenerators and by heating and cooling the gas during expansion and compression. It can be seen that the Ericsson cycle

represents the ideal limit of

cycle.

In actual cycles, of course,

is limited by failure to follow

cle, by “heat leaks” between

the Brayton

performance

the ideal cythe hot and

cold ends of the cylinder, by pressure losses

through heat exchangers and regenerators,

by miscellaneous mechanical losses, and by

imperfect heat exchange and regeneration

processes. Major development problems include the design of high-temperature heat

exchangers and regenerators which are easy

to manufacture and have displayed acceptable Iifetimes.

A problem unique to the Stirling an d

Ericsson cycles is the requirement for systems capable of ensuring that the workingfluid temperature remains constant during

the heat absorption and rejection processes.

A variety of schemes for accomplishing this

function have been proposed. One technique involves constructing pistons with a

series of fins which slide between mating

fins attached to cylinder ends maintained at

constant temperatures. These fins ensure a

large heat-exchange surface between the

constant-temperature source and sink and

the working fluid, even though the fluid

volume is changing.

Another design decision is the choice of a

working gas. The cycles operate most efficiently with a gas with high thermal conductivity, low density, low viscosity, and a

large change in volume when heated.

34 I t

can be seen from figure IX-29 that hydrogen

achieves the best theoretical performance.

It was selected by Philips and Ford Motor

Company for their prototype automobil e

engine.

Hydrogen is highly flammable and could

create a fire hazard if it escapes, although

the quantities used in small engines are extremely small. It may also be incompatible

with certain heater designs and some types

of heat pipes. (Heat pipes may be needed to

transfer thermal energy from a separate

heater.) A recent study by Philips and Ford

concluded that helium is a “requirement

when operating with the heat pipe since

hydrogen permeates the joints and ‘poisons’

the heat pipe.” 3 5

Theoretical work has also

been done on a variety of other working

fluids, including dissociating fluids and boiling and condensing fluids.

Design Alternatives

Prototype designs capable of approaching the ideal cycles are illustrated in figures

IX-30 and IX-31. The rhombic-drive device,

shown in figure IX-30, has been used by the

Philips Corporation since the 1930’s. It uses

a pair of pistons in the same cylinder and an

ingenious mechanical Iinkage to maintain

the proper phase between them. The newer

Philips design is shown in figure IX-31. This

system uses the working piston in one cylinder as the displacer for the adjacent cylinder, with four cylinders forming a closed

“W. R. Martini, Developments in Stirling Engines,

presented to the Annual Winter Meeting of the American Society of Mechanical Engineers, New York, N. Y,,

Nov. 26-30,1972, P.1

“R. J. Pens and R. D. Fox, A Solar/Stirling Total Energy System, published by Aeronutronic Ford Corporation.
Ch. IX Energy Conversion With Heat Engines ● 369

Figure IX-29. —Calculated Performance of a 225-hp Stirling Engine as a Function of the Specific

Power and Working Gas

56

48

40

32

125

1,500 rpm

400 rpm

I

24

0 10 20 30 40 50 60

Specific Power (h~jiiter)

SOURCE Samuels et al op clt , paqe 54

loop. The phas e is maintained with a

“swashplate” as shown in the figure.

A major problem for both of these devices

is the seal which must be made between the

working fluid (usually helium or hydrogen),

and the reciprocating shaft emerging from

the engine. The Philips design employs a

flexible membrane called a “roll-sock seal”

for this function, which links the piston shaft

to the cylinder wall with a flexible membrane (see figure IX-30).

The United Stirling Company of Sweden

uses a SIiding seal in most of their designs.

progress is being made, but these seals apparently still remain the major limit on

engine life and reliability. The seals could

present difficulties for total energy applications where they must be maintained at the

temperature of the hot water used for spaceconditioning; the life of the seals decreases

sharply at high temperatures.

70 80

The problem of these seals could probably be overcome for continuous power

applications if the seals were separately

cooled or if the engine were designed to be

sealed hermetically with an alternator. Such

systems, however, have not yet been designed. It can be seen from figure IX-32, that

if the energy available to these mechanical

drive systems changes, the engine speed will

change. A constant a.c. output from the system can be achieved in one of two ways: 1)

the engine speed can be permitted t o

change and the variable frequency output

rectified and inverted (as was necessary in

the case of the Brayton-cycle devices), or 2)

frequency control can be achieved by varying the pressure of the system using techniques developed for controlling Stirlingcycle automobile engines.

Some of the difficulties encountered by

the mechanical drive systems could be overcome if the free-piston systems shown in
370 ● Solar Technology to Today’s Energy Needs

Figure lX-30.— Philips Rhombic-Drive Stirling Engine

Power piston ~ml

Buffer space or

bounce space —-L II

— co

Regenerator

oler

u r=, / I

F ‘ ti ‘h

B

H

rJ /

Burner air i

Displacer

Cold spac

i’m

Piston 1

Buffer space

L

Pitch circle

of synchronizing gears &“--:’yl[!

Counterweight 1/ 1-

‘-

Displacer connecting rod

*Displacer yoke –

II

L

4

.-.=..-.r.l.r

Exhaust gas

approx. 200°C

Annular channel

Heating pipes

Cooling ribs

Regenerator

Cooling water 60° C

Hermetic

rolling diaphragm seal

Displacer rod

Piston rod

Piston yoke

Piston connecting rod

Crankpin

Crank radius

Rhombic gear unit

SOURCE: “Towards Cleaner Air: A Passenger Coach Powered by a Philips Stlrllng Engine,” N, V. Philips, Netherlands, January 1971.
Ch. /X Energy Conversion With Heat Engines . 371

Figure IX-31 .—Swashplate Stirling Engine

Expansion space

3

Heater

. ,.-J Regenerator

Cooler

Compress Ion space

p’

Dlacjram of Ihe double-actlnq type Stlrllrrg engine pr{nclple of

the double. acflng engine There IS a hot space—expansion

space—at the top and a cold one—compression space—at the

bottom of each of the cour cyllnders shown The hot space of a

cyl lnder IS connected to the cold through a heater, a regenerator,

and a cooler The pistons Pn of the cyllnders move with a

suitable phase shift between them In the case of four cyllnders,

as shown here, th IS shift IS 90”

Schematic diagram of a four cyllnder, double acting type Stlrhng

engine with swash plate drive One of the four cyllnders and one

of the four cooler regenerator units are shown In cross-section

In these engines, the movement of the pistons IS transmitted to

the main shaft by a swashplate

SOURCE Pictures and captions taken from R J Meller and C L

Splgl, “The Polenflal of the Phlllps Stlrhng Eng\ne for Pollutlon

Reduction and Energy Conservation “ presented at the Second

Symposium on Low Pollutlon Power Systems Development,

Dusseldorf, Germany, November 48, 1974

figure IX-33 are successfully devel -

oped. 36 37 38 These systems are thermal/me

chanical oscillators in which the working

piston and the displacer piston simply

bounce in the working fluid at a frequency

determined by the properties of the gas and

the mass of the pistons.

The designers of the ERG “thermal

oscillator” system claim to have developed

“W Beale, et al , Free Pfston Stir/ing Engines, Some

Model Tests and Simulations, SAF Paper 690230,

j anuary 1969

“W Beale, et al , Free Piston Engines, A Progress

Report, SAE Paper 730647, June 1969.

“G. M. Benson, Thermal Oscillators, Proceedings,

Eighth IECES Conference, Aug 14, 1973, Phlladelphla,

Pa

Figure lX-32.— Calculated Performance of a

Philips Rhombic-Drive Stirling Engine

General Design Data

Item

Shaft power

Effective efficiency

Engine shaft speed

Working fluid

Mean pressure

Max. cycle pressure

Min. cycle pressure

Expansion gas temperature

Compression gas temperature

Number of cylinders

Piston swept volume

Piston phase

Pressure phase

Piston diameter

Piston stroke

piston rod diameter

Water temperature in

Water flow

Heat pipe temperature

Engine length

Engine diameter

Engine weight

Value

22.4 kW

40°zY

2000 rpm

helium

200 atm

276 atm

141 atm

9650 K

335 ‘K

4

55 cm3

900

630

4.4 cm

3.5 cm

1.7 cm

303 ‘K

0.9 !/s

1,070° K

75 cm

45 cm

100 kg

System Efficiency at Various Power

Levels and Speeds

Power

5 10 15 20 25 kW

130

120

110

100

90

> 80

E

g 70

a

a 60 -

5

+ 50 “

40

30 -

20 -

10 “

1 1 1 1

200

ATM

c

100 J

ATM

50

ATM

o 500 1,000 1,500 2,000

Speed (rpm)

SOURCE H A Jaspers and F K du Pre, “Stlrllng Engine Design

Studies of an Underwater and a Total Energy Syslem.’ North

American Phlllps Corporation publication #739035, 1973 /ECEC

Record, pp 588.593

a free-piston system in which the frequency

of oscillation is independent of the load applied as long as the average working pres-
372 ● Solar Technology to Today’s Energy Needs

Displacer

piston

Po;er

piston

Bounce

Figure lX-33.– Free-Piston Stirling and Ericsson Cycle Designs

~-

Heat added

-r ~Regenerator

L+-Heatre’ec’ed

“m

Displacer—Power Piston System

Displacer

piston

Heat removed

I I Regenerators

volume Phasor ! I Heat added

1

/

L, cylinder

I

L

I

t

I I . u Power 1

piston

Phasor—Displacer— Power Piston System

SOURCE: Diagrams of free-piston devices shown above based on slmtlar diagrams In G M Benson, “Thermal Oscillators,” presented to 8th IECEC meeting,

August 14, 1973, Philadelphia, Pa.

sure is maintained in a sealed unit. T h e

energy applied to the load is automatically

adjusted as the pistons change stroke and

relative phase angle. 39 The use of the freepiston designs avoids the problem of mechanical linkages (having only two or three

moving parts), the need for starters (the

machines start themselves when heat is applied), and the problem of seaIing a reciprocating shaft. As a result, it may be possible

to develop a system which is inexpensive to

manufacture and has a long life and low annual maintenance. With pressures on the

order of 1,000 to 2,000 psi, and the use of gas

bearings where the working fluid provides

the necessary lubrication, efficiencies as

high as 70 to 80 percent of ideal should be

obtainable. (Some designers contend that 90

39G. M Benson, op. cit., p. 10

percent of ideal efficiencie s may b e

achieved, but this clearly will be extremely

difficult.)

One unique problem with the free-piston

design is that no rotating shaft emerges from

the system. The power is in the form of

linear oscillations of the working piston. The

piston may not move very far; a 1 kW unit

can move as little as 1 inch. ’” “Linear alternators” suitable for this application have

been successfully constructed, however,

and exhibited efficiencies comparable with

conventiona l alternator designs. ” 4243

‘“G. M. Benson, op. cit., p. 1.

41 Ibid,

‘

zWilliam Beale (Sunpower, Inc.), private communication, July 1976,

“William Beale, A 100-kVatt Stirling Electric Cenerator for Solar or So/id Fue/ Heat Sources, I ECEC 75,

Record, p, 1,020.
Ch. IX Energy Conversion With Heat Engines ● 373

Power is produced either by moving a conductor (in a design similar to a loudspeaker

voice coil) or by moving a magnet or flux

gate. One design approach is shown i n

figure IX-34.

While these devices have great promise,

relatively little work has been done on their

design in comparison with the more conventional designs. Their performance in operational configurations has not been extensively tested, and disagreements about their

practical achievable efficiencies and their

stability to varying loads and input conditions cannot be resolved until more work is

done. Working devices have been built,

however, and high efficiencies measured in

the laboratory. ” 45

The development of a heat-transfer surface which can transport energy at high

rates into a small cylinder head has proved

to be a difficult undertaking. The materials

required for this purpose must withstand

high pressure, as well as exposure to oxidizing hot gases on one side of the heatexchange surface and hydrogen on the other

side. Devices capable of accomplishing this

function can be made, but they must use

alloys which are relatively expensive in comparison with the mild steel used in conventional engines— and in many cases, the

designs appear to be difficult to manufacture. Heat pipes may be able to solve some

of the problems faced in this area by providing rapid heat transfer in a system which

does not produce a large pressure drop in

the working fluid.

46 The development o f

ceramic heat-exchange materials wouId be a

great asset to the technology, since ceramic

devices would be able to operate at

high temperatures (i. e., 2,0000 F) and it

be possible to manufacture them with

cost, mass-production techniques. The

very

may

lowhigh

“G M Benson, op clt , p 14

4SBeale, private communication, j uly 1976

4’S G Carlqulst, et al , “Stirling Engines Their Potential Use In Commercial Vehicles and Their Impact

on Fuel UtlllzatIon, ” lnstn Mech .Engrs, 1975, p 35

“W A Tomazlc and James E Calrelll, Ceramic Ap

p/ications In the Advanced Stirling Automotive Engine

(ERDA/NASA 1011/77/2, p 6)

operating temperature permitted would also

increase the potential efficiency of the

system. DOE is sponsoring research to develop a ceramic heat exchanger for Stirling applications beginning in FY 1978.47

An interesting sidelight to the Stirling- and

Ericsson-cycle devices just described is their

ability to integrate engines and heat pumps

into a single device. Two approaches to this

design, using the free-piston concept, are

shown in figures IX-35 and IX-36. This design

can be modified to include electric generation by using the “phaser” pistons as linear

alternators, thereby making the device an

attractive total energy system. The system is

also attractive in that the performance of

the heat pump does not drop rapidly as outdoor temperatures decrease (as is the case

with conventional electric heat pumps). ’n 49

An Ericsson-cycle heat pump would probably have a higher efficiency than commercial heat pumps, but the impact of the new

cycle on overall system performance would

not be dramatic since most of the losses in

current heat-pump systems result from the

need to heat (or cool) the refrigerants to

temperatures far above (or below) room

temperature so that the room air-flow will

be kept to comfortable levels. Heat exchangers and the requirements of fans are

the second greatest source of inefficiency. 50

These effects reduce the performance of

contemporary heat pumps by more than a

factor of five. The efficiency of the compressors used in contemporary heat pumps

is typically 75 percent of the ideal Carnot ef -

ficiency.

It is also possible to operate a Stirling

engine as a standard total-energy system, as

“Paul R. Swenson, Consolidated Natural Gas Service Company, Cleveland, Ohio, “Compet[tlon coming

in Heat Pumps: Gas-Fired May be Best in Cold

Climate, ” Energy Research Reports, 3(5], Mar 7, 2977,

p 2

‘

g

’’ Advanced Gas-Fired Heat Pumps Seen Cutting

Heating Bills in Half, ” Energy Users Report 188

(3/7/77), p 27, Bureau of National Affairs

50W, A. Spofford, “Heat-Pump Performance for

Package Air Source Units,” ASHRAE /ourna/, April

1959,
374 ● Solar Technology to Today’s Energy Needs

Figure lX-34.— Sunpower Systems Free-Piston Stirling and Ericsson Cycle Design Approach

Liquid filled —

cool ing fin

II

.

~ Cooling air fan

Cooling air outlet

~1-li U . .

k ‘“J, ,J ,, ;::;: f’:d’”g

9

“ dJJF,e:’:lnding A

41

l’” Jli . . .. ,’

,.

,..

.,.

. . -Spring suspension

II

— Draft shroud

“ “ ‘“+’’’’’”

~

Displacer rod

I

Liquid filled

‘Tcoolina fin

Cylinder sleeve _

Displacer seal

ring

<

Displacer II

u ’ -

●

Regenerator

~~

,.

matrix

. .

,,

,.

,.

., .

wL Cooiing ai r

Ilk#

I Liquid filled

IIN cooling fin (air side)

Cooling fin (gas side)

JJ

&

Regenerator matrix

i

,:

-,

..- .“

$ ,,

. .

.~

::~Ceramic filler

7.”

HI Annular gas

I I ( II I 1 / passages (finned)

Heat addition

SOURCE: W T, Beale and C. F. Rankine (Sunpower, Inc.), “A 100 Watt Stirling Electric Generator for Solar or Solld Fuel Heat Sources,” IOth IECEC, August

1975, Proceedings, p. 1020.
Ch. IX Energy Conversion With Heat Engines ● 375

Figure IX-35. — Free-Piston Total Energy System

Qout (warm)

f

~

Displacer / Cylinder

-

1

/

Qin

1 1

(hot) Compressor cylinder Qin (cold)

1 1

Bounce vol. Bounce vol.

TH Tc

o3

. .

=

= o4

Note: Only phasor position determines working

and bounce gas pressures (Pw + pb) SinCe opposed motion of hot and cold displacers (H + C)

produces a constant Pw

.

SOURCE. G M Benson (ERG), Thermal Oscillators, op clt (U.S. patent

No. 3,928,974).
376 . Solar Technology to Today’s Energy Needs

Figure lX-36.— Free-Piston Total Energy System

Heat

5,700

input

Btu/hr

Heat rejection

41,700 Btu/hr

t

88°F

90”F

t LI ‘a K1~ ‘- / 24” ID

1,500° F metal llnOperating

frequency

10 H

A

1 ’

1’

1’

1

1

;1

\

I

I —

~50”F

Cooling power

36,000 Bt u/hr

~ 45°F

200 Annuli 0.010” thick 1 , , ,

{

I

Pmax. = 261.7 I Pmin. = 107.2 -

17.7” STR.~ 17.7” STR.

I

id

lb.

PAV = 148.1 psia

L

Optimized preliminary design for a heat-operated heat pump

SOURCE W R Martlnl (Unwers!ty of Washington, Rlchland), “The Free-Displacer-Free-Piston Stlrllng Engine—Potential Energy Conserver,” 1975 IECEC

Record, pp 9951,002, 1976.

shown in figure IX-37. Space heat is provided

from engine waste heat. Another approach,

currently being supported by the American

Gas Association, uses the piston of an

Ericsson-cycle device to drive a sealed freon

compressor.

51 WilIiam Beale of Sunpower,

inc., has proposed still another alternative

which is being investigated by the American

Gas Association. His design would use the

working piston in a free-piston device as the

compressor for a Rankine-cycle heat pump.

The working piston contains a mass whose

inertia changes the volume available to the

“Dr. C. H. Benson, ERG, private communication,

Feb. 2,1977.

refrigerant inside the working piston as the

piston oscillates.

5 2

The refrigerant enters

and Ieaves this compression volume through

flexible metal tubes which provide a leakfree path for the refrigerant through the

helium-filled spaces surrounding the piston.

Performance

The performance of a number of the devices surveyed by the Jet Propulsion Laboratory in its review of potential automobile

engines is summarized in table IX-8. All of

-5~W111 lam Beale, President of Sunpower, I nc,

private communication.
Ch. IX Energy Conversion With Heat Engines Ž 377

Figure IX-37 .—The Philips Design for a Stirling Engine Total Energy System

. Preheater

E

SOURCE H A Jaspers and F K du Pre, .SIfrllng Engine Design Stud/es of an Underwater Power System and a Tofa/ Energy Sysfern, (N V. Phll(ps

publtcatlon)

these devices use mechanical linkages of

some sort. The efficiency of operating engines averages between 24 and 30 percent

(about 45 to 50 percent of ideal Carnot efficiency).

An optimized engine operating at its most

efficient speed could, according to these

estimates, produce 43 percent efficiency

operating between 1,4000 and 1600 F (about

65 percent of ideal efficiency). Achieving

this high efficiency, however, would require

operating the engine at less than its maximum designed power, thus increasing its

cost. The performance reported for freepiston devices has varied considerably because many different heat exchangers, regenerators, and thermodynamic cycles are

being examined. Consequently, it is much

too early to make a reliable estimate of the

efficiency of commercial systems. The efficiencies of devices constructed to date by

the Sunpower, Inc., group have been relatively low (10 to 30 percent cycle efficiency

or 16 to 48 percent of ideal efficiencies)

(table IX-9).

The performance of free-piston devices

reported by Energy Research and Generation Corporation (ERG) is shown in table

IX-10. These reports claim measured “indicated” efficiencies as high as 87 percen t

of ideal Carnot efficiency. In the device

operating between 1,4000 and 120°F, this

results in a cycle efficiency of 60 percent.

The feasibility of achieving these efficiencies is corroborated by estimates made by a

group studying Stirling engines in the joint

Center for Graduate Study at Richland,

Wash., and by Beale of Sunpower, Inc.,

although there appears to be some disagreement as to how far development has progressed towards this objective. 5354

The performance, of course, is largely sensitive to design details, including the size

and design (and hence the cost) of heat ex5]W R Martini, The T/rerrnohydrau/ic Converter ,

prepared for the joint Center for Graduate Study,

Richland, Wash , Mar. 4, 1975

5 4W. Beale, Sunpower, Inc , private communication, July 1976,
378 • Solar Technology to Today’s Energy Needs

Table IX-8.—StirIing Engine Characteristics

24

30

35

2,000

N/D

N/D

Auto

He

3,200

4

200

3,000

253

1,000

1,260

108

30

35

76

29

32

88

changers used, the gas pressure used in the

cycle, the exact thermodynamic cycl e

chosen, and other variables.

Performance With Waste Heat

As noted earlier, Stirling devices have a

great advantage in total energy applications

because a very large fraction of the energy

not used by the cycle appears in the cooling

water. This is shown quantitatively for systems burning fossil fuels in figure IX-38. In a

solar application, the percentage of energy

recoverable in the coolant water would be

even higher, given that there would be no

losses in the exhaust. The performance of

Stirling- and Ericsson-cycle devices operating at different coolant temperature is

shown in figure IX-39 for two different

assumptions about engine-generating efficiency.
Ch. IX Energy Conversion With Heat Engines . 379

Table IX-9 .—Performance of Free-Piston Stirling

Engine Designs of Energy Research and

Generation Inc.

ERG ERG Allison

50

.41

1220

170

62

80

118

1.79

4.81

1985

144

50

13.1

System Costs

It is impossible to estimate the costs of

Stirling and Ericsson cycles with any precision, since no practical devices are on the

market. The cost will also depend on the efficiency and the lifetime expected of the

system. I n general, efficiency is improved

Figure IX-38.— Heat Balance for the Stirling

and Diesel Engine

Friction 1000/0 fuel

heat input

Exhaust and

rad iat Ion

II I Coollng

water

Stirling Diesel

SOURCE R J Me[jer (N V Phillps), ‘The Phll(ps Stlrllng Engine,”

De Ingenieur (621 41), page 21

Table IX-10.-Performance of Sun Power

Free-Piston Devices

with large heat-exchange surfaces, but heat

exchangers are expensive.

There could be some difficulty in adapting current designs to mass-productio n

techniques since many current designs require complex heat exchangers which would

need many separate welds and brazements.

It should be possible to overcome this difficulty with advanced heat-exchanger designs, but the question of costs cannot be resolved until a production unit is designed.

Estimates made by the Jet Propulsion

Laboratory in their survey of automobilepower systems indicate that a “mature ”

Stirling engine, operating at a temperature

of 1 ,400 “ F, would cost approximatel y

$14/kW wholesale, and would sell for approximately $18/kW at the retail Ievel. 55

(This, of course, assumes production on the

scale of current automobile product ion.) A

further study of the adaptations needed to

install a 42-percent efficient Stirling devic e

in a solar energy application resulted in an

estimate of about $38/kW for the engine,

$27/kW for the alternator (installed on t h e

engine), and about $27/kW for miscellaneous switching equipment and controls.

5 6

This results in a total cost of about $92/k W

55ArI Autorrrobi/e Power S ysterns Evacuation, Jet Propulsion Laboratory, Volume 11, pp 11-12

“Richard Caputo, J PL, Program Manager, Comparative Assessment of Orbital and Terrestrial Power

Systems, p.24
380 •Solar Technology to Today’s Energy Needs

Figure lX-39.— Electric and Thermal Output of a Stirling Engine

c

- — — a&ailabJa for process heat

— (electric output~(input energy)

70 —

— - — 60Y0 Carnot

6 0—

—— —— ————

——

——~

50.-

~-

~A~arn~ — --- ~

 -

-

90°A Carnot

40 — }

-—— —

30 — 60% Carnot

20 1 -

10. I I I I I I I I

100 150 200 250 300 350 400

Cooling Temperature ‘F

Assumptions:

inlet temperature = 1400°F

Generator efficiency = 90%

energy not recoverable = 59’0

SOURCE, Prepared by OTA.

(all prices are given

peak- power output;

in terms of price peraverage power would

be substantially lower). These prices also do

not include the cost of the receiver and heat

pipe needed to transmit solar power to the

engine.

Another estimate of the cost of a Stirling

engine/generator set was made by Philips

and Ford Aeroneutronics for their proposal

to construct a solar, total energy system in

Disney World. This estimate for an engine/-

generator and switch-gear amounted t o

$400/kW, with an aside noting that this

could be reduced to $100/kW if large-scale

production were undertaken .57

57pOns, et al., Op. citr p“ 13’

The cost of free-piston devices could be

lower than those of the mechanically coupled systems because of their inherent simplicity, but again the lack of commercial

devices makes cost estimates difficult. The

Energy Research and Generation Corporation has estimated that their free-piston

design is amenable to mass-production techniques and could be produced for about

$30/kW, with an additional $10/kW for the

linear alternator. 58

Another way of estimating the cost of the

Stirling-engine devices, manufactured at

moderate production rates, is to compare

‘aGlen Benson, Energy Research and Generation

Corporation, private communication, December

1976.
Ch. /X Energy Conversion With Heat Engines ● 381

them with the cost of conventional gasolineand diesel-powered engine-generator sets.

Figure IX-40 indicates that the Stirling devices with mechanical linkages should have

a weight per-unit-of-power which is somewhere between gasoline and diesel engines.

Assuming that the Stirling devices ar e

roughly of the same complexity, figure IX-41

can be used to estimate costs of about $75

to $150/kW for shaft output Stirling engines

of about 100 kW capacity.

Figure IX-40. —Weight-to-Power Ratios of

Engines With Internal Combustion and of

Stirling Engines

100

10 A -’””s

B

-)

A

c Stirllng engines

B

Petrol engines c

1

1 10 ~ 100

kW

A A Stlrllng enqlnes present laboratory types

B Laboratory models to be expected w Ith,n a few years

C Stlrlinq engines developed for vehicles

Welqht to-power ratios of engines with Internal combustion and of

Stlrllnq engines

SOURCE

R J Meyer Comblnaton of Eleclr[c Heal Battery and Stirlrng

Engine—An Alternative Source of Mechan mal Power, reprtntcd

from Denkschrlft Elcktrospe[r herfahrzeuge ‘ Volume 1 Ill 969

Figure 1X.41 .—Cost of Diesel Engines

COST OF DIESEL ENGINES

700

1

~ Onar! diesels

~=

600 t I r-l’ Llstner diesels

~ 500

*

* 400

z

z

300

f~u

aasollne General Motors

‘t “+C ;ng[ne generatars ~ diesels

100 All Is Chalmers 1 1

~ diesels , — .~ . . -. .~

1 10 100 1000

Engine/Generator capac, ty )kW)

SOURCE Prepared by OTA using manufacturer’s data

Free-piston designs could weigh significantly less than the mechanical devices

shown in the figure. Dr. Benson of ERG has

estimated that their device could weigh as

little as 5 lbs/kW (2.3 kg/kW). 59

State of the Art

Engines based on the Stirling and Ericsson

cycles have been in operation since the early 19th century, The Stirling engine was

patented in 1816 by a Scottish clergyman,

John Stirling; Ericsson-cycle devices were

patented a few decades later. (The Ericsson

cycle is named for the Swedish-American inventor, John Ericsson, who, among his other

accomplishments, was the designer of the

Union ship, The Monitor.) These earl y

designs used air as the working medium and

were expensive, heavy, and relatively inefficient—since the designers lacked both materials and analytical methods capable of

optimizing the design of thermodynamic

cycles.

Interest in Stirling engines was revived in

1938 by the Philips Corporation of th e

Netherlands, when that company wa s

searching for an engine to burn a variety of

fuels and provide quiet and reliable powe r

to military radio receivers. 60 The company,

one of the world’s largest multinationa l

firms, now has over 100 people working on

the development of Stirling engines. Many

world patents for Stirling engines are held by

Philips, and the vast majority of work which

has been done on Stirling devices in this century has been done either by PhiIips or under

license from Philips. The company has several well-developed engine designs, some of

which have operated over 10,000 hours without failures. 61 They have been used to power

a number of vehicles including boats and a

small bus. The basic development engine

59 Benson, ibid.

‘“R, J. Meijer and C. L Spigt, The F’oter-rtia/ of the

Philips Stirling Engine for Pollution Reduction and

Energy Conservation.

“Norman D, Postma, et al,, The Stir/ing Engine for

Passenger Car Applications, Ford Motor Company

publication.
382 ● Solar Technology to Today’s Energy Needs

has been a 25-hp device using two rhombicdrive cylinders. About 30 to 40 of these

engines have been built by Philips or are

under Iicense from Philips.62

The U.S. National Bureau of Standards is

testing one of the few Philips engines that is

outside of the Netherlands to measure its

performance in total energy applications. 63

The Philips work stimulated interest in

Stirling equipment by a number of different

companies. The General Motors Company

had an extensive program in the development of Stirling engines which began as a

cooperative program with Philips. Research

and design studies were conducted on a

number of different engine designs in -

cluding free-piston devices. The company

had accumulated over 28,000 hours of engine running-time experience between 195 9

and the abrupt termination of the project. b

’

In 1972 the Philips Company entered into

a contract with the Ford Motor Company to

develop a Stirling automotive engine. Work

has been underway since then. The program

began with an attempt to use a swashplate

Stirling engine with a 1973 Ford Torino.

Problems have apparently developed with

the original approach, however, and progress is slower than had been expected.

The United Stirling company of Sweden

has also done extensive development work

on Stirling equipment and is apparently

planning to have a device ready for fieldtesting in Swedish iron mines by 1979. 65 T h e

company plans to market 40-, 75-, and 150-

kilowatt engines shortly thereafter for use in

‘

2 Pens, op. cit , p 11.

“D. Diddion, National Bureau of Standards, private

communication, December 1976

“W H. Percival, Historical Review of Stir/ing Engine

Deve/oprnent in the United States from 1960 to 1970,

prepared for the ERD,A(EPA contract 4-E840595), July

1974, page 124,

‘sHallare, Bengt, Director of Corporate Planning

and Marketing, United Stirling, et al., “Development

of Stirling Engines in Sweden and Their Application in

Total and Solar Heated Energy Systems. ” Paper

delivered to the 1977 International Solar Energy Conference and Exhibit, Palm Springs, Fla., 1977. Proceedings published by the Northrop University Press.

mine-pumping operations (where their low

emissions, fuel economy, and quiet operation should be great benefit), in total energy

systems for homes, and for automobiles and

buses .

66 The United Stirling devices use a

“sliding seal” instead of the “roll-sock” seal

employed by most of the PhiIips engines.

The Thetford Corporation of Michiga n

recently formed a joint venture wit h

Sweden’s Forenade Fabriksverken (FFV) to

manufacture a Stirling total-energy system

for recreational vehicles which the company

hopes to have on the market in 1978.”7

In addition to Philips and the United Stirling Company of Sweden, MAN of Germany

has accumulated many years of experience

with Stirling devices, some of it based on

Philips’ designs.

Much less work on Stirling and Ericsson

cycles is being done in the United States.

The Atomic Energy Commission and the

Heart and Lung Institute at the National institutes of Health initiated a program in

1966 to develop an artificial heart. Several

designs were proposed using electric motors

and Rankine and Stirling engines. The program attracted several U.S. companies, including Aerojet, Thermo-EIectron Corporation, ERG, Inc., Air Products and Chemicals,

Inc., and Westinghouse Astronuclear (under

contract with Philips). 68

Work on novel engine designs for transportation and automotive applications is being performed by the Energy Research and

Generation Corporation, Sunpower, Inc.,

and by a variety of university groups. The

work at Sunpower is based, in part, on funding from the American Gas Association

with the objective of developing a heat

pump able to operate from natural gas. The

company is also working under an ERDA

grant to develop an engine using a radioactive source to provide electric power for

66W. H. Percival, U.S. representative of the United

Stirling Corporation, private communication, May 6,

1977.

“Ann Arbor News, Mar. 25,1977.

6’William Beale, A Stir/ing-Hydrosta tic Drive for

Srna// Vehic/es, provided by Sunpower, Inc.
Ch. IX Energy Conversion With Heat Engines Ž 383

spacecraft.

69 Figure IX-42 shows the Sunpower device installed in a solar collector.

Work on Iinear alternators suitable for attachment to Stirling- and Ericsson-cycle

devices for electric-power generation has

been performed by the Energy Research and

Generation Corporation and by the Mechanical Technology Corporation. Both groups

have tested operational designs, but neither

firm has a unit on the market. Work on the

use of Stirling engines for transport is also

being done by the Sunpower Corporation,

Energy Research and Generation Corporation, and Polster.70

“G Benson, Thermal Oscillators, op clt

7 0N E Polster and W R Martini, “self-starting, lntrinslcal Iy Control led Stirling E nglne, ” IECEC Record,

PP 1,511-1,518, 1976

Although a number of groups have investigated Stirling- and Ericsson-cycle devices, the engines must be considered to be

in a relatively primitive state of development. The alternative cycles have benefited

from many years of careful design work,

while most Stirling designs have remained in

the laboratory. No Stirling engine is being

produced on a large scale anywhere in

world.

OTHER HEAT-ENGINE DESIGNS

The Thermionic Converter

the

The thermionic device shown in figure

IX-43 can operate at very high temperatures

Figure IX-42 .—200-Watt, Sun power Stirling Engine, Mounted in Concentrating Collector

i i

Photo credff .Sunpower, /nc
384 ● Solar Technology to Today’s Energy Needs

Figure lX-43.— Identification of Thermionic Converter Components

Thermionically Interelectrode

space emitted electrons

\’———— ~ Vacuum or vapor

Hot emitter

Cold collector

Qin

—

n. -

— I

v Heat

source

Electrical

feedthru

— load

SOURCE Thermoelectron Corporation

Enclosure

and can achieve extremely high-power densities (on the order of 2 to 10 watts/cm2 o f

receiver surf ace).” The hot emitter and the

cooler collector of a therm ionic converter

are separated by a vacuum or by an ionized

gas. A current can be sustained if the hot

side of the diode emits electrons at a greater

rate than the cold side. EIectrons evaporated from the emitter flow across the interelectrode gap to the collector, where they

condense and are returned to the emitter via

the electrical load. Some of the thermal

energy transferred from the hot to the cold

side of the diode is carried directly by electrons, which are the “working fluid” of this

“William C, Reynolds and Henry C, Perkins, Engineering Thermodynamics, McGraw H ill, 1970, p, 309.

engine. The heat flow is thus translated

directly into a flow of electricity.

Therm ionic energy conversion has a

number of desirable characteristics: 1) no

moving parts, 2) heat rejection at relatively

high temperatures, 3) lends itself to modular

construction, 4) potential for efficiencies up

to 40 percent, 5) heat input in an intermediate temperatur e range (1 ,2000 t o

1,8000 K), 6) the mechanical simplicity associated with no moving parts implies reliability, and 7) the high temperature of heat

rejection makes therm ionic converters well

suited for topping steam powerplants, because the heat rejected from the collectors

is available at a high temperature to generate steam for conventional turbomachinery.

Efficiencies as high as 5 to 15 percent

have been reported for devices working be-
Ch. IX Energy Conversion With Heat Engines • 385

tween 1,160” and 2200 F (13 to 38 percent of

ideal Carnot efficiency) .72 A curve of performance predicted for advanced designs of

therm ionic converters is shown in figure

IX-44. It can be seen that high efficiencies

are possible if the losses which now limit

performance can be reduced.

The feasibility of therm ionic conversion

has been demonstrated with a variety of

hydrocarbon, solar, radioisotope, and reactor heat sources. Stable in-pile operation has

been achieved for over 16,000 hours. T h e

Soviet Union has progressed to the third

generation in-core therm ionic reactor with

electrical outputs of over 7 kilowatts.

Figure lX-44.— Effect of Collector

Temperature on Thermionic Efficiency

Emitter

temp =

1,700 K

1,600

1,500

1,400

10 1 I I

700 800 900 1000

Collector temperature (K)

SOURCE Thermo Electron Corporation

72 Huff man, Thermo-E Iectron Corp , private communication, j anuary 1977

While a good base of high-temperature,

thermionic-conversion technology exists,

thermionics has yet to achieve practical application with fossil fuels because the emitter temperatures currently required for competitive power densities and efficiencies

limit the operating life of the “hot shell”

(i.e., the protective structure which isolates

the converter, per se, from the combustion

atmosphere) to several hundred hours. I n

order to reduce the operating temperatures

of converters to levels where the hot shell

will have greatly extended life while maintaining converter efficiency, it is necessary

to develop improved emitter and collector

surfaces, as well as decrease the plasma

losses occurring as the electrons flow across

the interelectrode space. Reasonable progress is being made in both areas.

Thermoelectric Conversion

Electricity can also be generated directly

from a source of high-temperature thermal

energy using a solid-state “thermoelectric”

junction. 73 These devices, which operate on

the same principle as thermocouples, are

frequently used to power spacecraft using

isotopes as power sources. Devices operating with an isotope source of 1,000“C

(1,832 0 F) are capable of efficiencies on the

order of 3 to 6 percent. 74

The Nitinol Engine

Thermal energy is converted into mechanical work when a heated metal expands, A

nickel titanium alloy called Nitinol developed by the Naval Ordnance Laboratory

(Ni + Ti + N. O. L.) in 1958 has unique thermal properties which can be used to construct a primitive heat engine— one design is

shown in figure IX-45. Nitinol deforms easily

at low temperatures but returns to its

original shape with considerable force when

heated. Several working devices have been

71P Rouklove, Tests and Evaluation of Mu/tihun~re~ kVatt Thermoelectric Generators at /PL, 12th

IECEC Conference, p 1,287

“j E Boretz, Reactor Hybrid-Organ/c Ranhine Cyc/e E/ectric Power 5 ys terns for Space App//ca tfons,

12th I ECEC Conference, p 1,318
386 • Solar Technology to Today’s Energy Needs

Figure lX-45.—The Nitinol Engine

SOURCE The CoEvo/utIon Quarter/y, Spring, 1975, p. 70

constructed by Ridgeway Banks at the Lawrence Livermore Laboratory.

Osmotic-Pressure Engine

Thermal energy can also be converted to

mechanical energy in the osmotic-pressure

cycle. The heat is used to distill a dilute

solution into pure solvent and a concentrated solution. Energy can be recovered if

the solvent and concentrated solutions are

pumped into different sides of a chamber

separated by a semipermeable membrane.

The solvent is forced across the membrane

with a pressure equal to the difference between the osmotic pressures and hydraulic

pressures of the fluids on either side of the

membrane. The osmotic pressures can be

quite large. A saturated solution of NaCI in

water, for example, has an osmotic pressure

ar input

Nitinol w

loops

i ire

~ Cold bath

of 380 atmospheres (about 4,000 m o f

water). Every cubic meter of water sent into

the reaction chamber with a saturated NaCl

solution, therefore, has a potential energy of

about 11 kWh. The fraction of this energy

which can be retrieved in a practical system

has not been established, although some

preliminary design work has been done on

membrane reaction chambers. 75 76 Membranes suitable for use in these systems are

commercially available. Du Pont, for exam75S. Loeb, “Production of Energy From Concentrated Brines by Pressure-Retarded Osmosis: 1,

Preliminary Technical and Economic Correlations, ”

)ourna/ of Membrane Science 1 (1976), p, 49.

7’ S. Loeb, et al., “Production of Energy From Concentrated Brines by Pressure-Related Osmosis: 11. Experimental Results and Projected Energy Costs,” /ourrra/ of Membrane Science, 1 (1976), p. 249.
Ch. IX Energy Conversion With Heat Engines . 387

pie, has a membrane called “Permasep,” designed for us e in desalinization plants,

which costs about $4/m2 of active surface.

One square meter of this surface is able to

pass about 0.16 m3

/day when a pressure difference of 400 atmospheres is developed

across the surface. 77 Waste heat can be

recovered from the system via the condenser of the distillation unit.

ENVIRONMENTAL AND SAFETY PROBLEMS

FLUOROCARBONS

Many of the currently available low-temperature heat engines employ fIuorocarbons

identical to the refrigerants now used in

home and small industrial refrigeration and

air-conditioning equipment: F-1 1 (CCI3F),

F-12 (CCl 2F2), and F-22 (CHCIF2). Thes e

substances have great chemical stability at

low temperature, but this very chemical

stability may lead to severe environmental

problems. Because fluorocarbons do not

decompose once released into the environment, they remain in the atmosphere and

eventually react chemically with the Earth’s

ozone layer, possibly reducing the ability of

the ozone to shield the Earth’s surface from

the Sun’s ultraviolet Iight. 78

The environmental, biological, and health

effects of stratospheric ozone changes are

only now being discovered. Some scientists

suggest that changes in stratospheric ozone

levels could cause changes in the Earth’s

climate, including changes in temperature

and wind patterns. 79 The health effects of

changes in the stratospheric ozone are not

fully understood. The decreased ozone layer

results in an increased incidence of ultraviolet radiation on the Earth’s surface. Some

evidence supports a correlation between

ultraviolet radiation and malignant melanoma, the most serious, often fatal, form of

skin cancer.80 Studies have indicated that in77S Loeb, op cit , 11, p 254.

“M. J Molina and F J Rowland, “Stratospheric

Sink for Cholofluoromethanes Chlorine Atom

Cata Iyzed Destruction of Ozone, ” Nature

249.810-812, 1974.

79NAS Report, pp. 72-78

‘ONAS Report, pp 81-89

creased ultraviolet irradiation results in increased incidence of nonfatal, nonmelanoma types of skin cancer in humans. 81 Increased ultraviolet radiation may also have

some adverse effect on human eyes and

eyesight ,

82 and possibly on growing plants,

as well.

In addition to the ozone depletion caused

by the release of fluorocarbons into the environment, and the coincident human health

effects, direct health effects from exposure

to fluorocarbons have been reported in

various animals. These effects include influences upon the respiratory and circulatory systems in mice, rats, dogs, and

monkeys. 83 Research into the environmental

and health consequences of fluorocarbons

has received impetus from concern over the

widespread use of fluorocarbon propellants

in aerosol sprays.84

Some fluorocarbons leak into the environment from facilities which manufacture refrigeration equipment and from abandoned

or malfunctioning units. Estimates indicate,

however, that less than 3 to 6 percent of the

fluorocarbons lost into the environmen t

come from this source, even though the refrigerants market constituted 28 percent of

8’ IMOS Report, p. 70.

821 bid., p. 74,

83D. M. Aviado, “Toxicity of Aerosol Propellants in

the Respiratory and Circulatory Systems [X, Summary

of the Most Toxic: Trichlorofluoromethane (Fll ),”

Toxicology, 3:311-319, 1975.

“See e g , M. B. McElroy, “Threats to the Atmosphere, ” Harvard Magazine, 78:1 9-25, 1976; J E igner,

Unshielding the Sun... Environmental Effects, Environment, 17:1 5-18, 1975; A.K.A. ed, Unshielding the

Sun. . .Human Effects, Environment, 17:6-14, 1975
388 ● Solar Technology to Today’s Energy Needs

the total fluorocarbon market in 1972 .

85 8 6

Recent studies indicate that losses from

refrigeration equipment can be reduced,

especially those from automobile, home,

and commercial air-conditioning units. 87

The use of a freon-based heat engine to

provide solar air-conditioning would in -

crease the amount of freon in a typical

home by a factor of 2 to 3. A house using a

freon-based engine to provide 100 percent

of residential electrical and air-conditioning

needs would need 5 to 6 times more freon

than a conventional house.

The environmental impact of this increase

in fluorocarbon use (independent of other

fluorocarbon uses such as aerosol pro -

pellants) is yet to be fully evaluated, but

because of the possibility of severe environmental damage either from fluorocarbons or their consequent ozone depletion,

these impacts are being analyzed. ”

Although ozone levels fluctuate worldwide, it is believed that an overall depletion

has occurred, perhaps because of fluorocarbon usage. 89 The effect of this level of depletion is still controversial. It appears, however, that the use of fluorocarbons in onsite

energy production will not be a major problem. This is because only a low percentage

of environmental fluorocarbons result from

loss due to use as a refrigerant. Until a replacement fluid for fluorocarbons is found,

an attempt should be made to minimize

their escape into the environment.

a’Ha/ocarbons: Environment/ Effects of Cho/c

f/uorornethane Release, National Academy of

Science, Committee on Impacts of Stratosphere

Change, Washington, D. C., 1976 (hereinafter, NAS

Report), p. 16. Fluorocarbons and the Environment,

Report of Federal Task Force on Inadvertent Modification of the Stratosphere (l MOS), June 1975, (here

inafter, IMOS Report), p.91.

OSIMOS Report at page 88, P. H. Howard and A

Hanchett, “Cholofluorocarbon Source of Environmental Contamination, ” Science, 189:21 7-219, 1975.

8TIMOS Report, P. 93

‘“Manufacturing Chemists Association, Research

Program of Effect of Fluorocarbons on the Atmosphere, Dec. 31, 1976, and NAS Report,

OglMOS Report, P. 380.

Under the Toxic Substances Control Act

(Public Law 94-469), the process of regulating use of fluorocarbons is beginning because of the possibility of extremely severe

environmental effects . In the Federa l

Register of March 17, 1978, the Environmental Protection Agency, Food and Drug Administration, and Consumer Product Safety

Commission issued regulations stating that

it will be illegal to: a) manufacture aerosol

cans containing fluorocarbons after December 15, 1978, and b) introduce such containers via interstate commerce after April

15, 1979. Uses of fluorocarbons in refrigeration, including onsite solar energy systems,

wilI be regulated later. Use of fluorocarbons

in onsite solar energy systems is merely one

category of use in refrigeration units, however, and as such will not

mediate regulation.

NOISE

Because the equipment

be subject to imfor onsite energy

production may be located in or near living

or working quarters, the noise emitted by

these systems must be considered as an environmental impact. Solar collectors and

energy-storage systems are silent except for

the low rumble of intermittent pumps and

flowing water, but in systems which employ

gas turbines and other types of heat engines,

noise could be a problem. Without noise

suppression, a gas turbine of a size sufficient to generate all electricity for a single

home would emit about as much noise as an

unmuffled internal combustion automobile

engine at full throttle. ’” However, the noise

from gas turbines is readily suppressible to

levels quieter than a common household

furnace fan– less than 40 decibels.” This

suppression is a normal part of commercial

turbine installations. In a total energ y

system (a system which employs waste heat

from energy production for space heating

uses), noise suppression of the gas turbine

90108-1 20d Ba, at 10 feet,

“Patrick G. Stone, Garrett Corporation, Washington, D. C., personal communication, Feb. 11, 1977,
Ch. IX Energy Conversion With Heat Engines ● 389

can be accomplished using a waste-heat

boiler, reducing the noise to acceptable

levels without added installation costs.

WATER USE IN STEAM CYCLES

The solar energy systems of a small community or industrial plant, on the order of 15

MW(e), may employ water or steam in energy conversion.

Although this water will not be polluted

by chemicals during this process, it wil l

return to the environment with added heat.

In areas of water shortage, the requirement

for replacing the amount of water lost could

constitute a major problem. This is particularly true in dry, sunny climates where

solar systems have other advantages, and

should be considered prior to installation of

such a system. Water requirements would

be about the same as for a fossil steamplant

of similar capacity.

SODIUM AND POTASSIUM VAPOR

Some of the proposed high-temperature

storage schemes require heat pipes which

use sodium or potassium vapor as their

working fluid. While only very small quantities of these substances are required, they

could have minor adverse environmental

impacts, although both of these vapors are

presently employed in street lighting, and no

adverse use impacts have been reported.
Chapter X

ENERGY CONVERSION WITH

PHOTOVOLTAICS
Chapter X.— ENERGY CONVERSION WITH PHOTOVOLTAICS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .393

Photovoltaic cells. . . . . . . . . . . . . . . . . . . . . ...395

Cells Designed for Use in Concentrated

Sunlight . . . . . . . . . . . . . . . . . . . . . . . . . .. .400

Optimizing Conventional Silicon Cells

for Use in Concentrated Sunlight .. ...400

Interdigitated Back-Contact Cells . . . . . . .400

Gaiiium-Arsenide Cells. . ..............401

The Vertical Multifunction Cell . ........401

Horizontal Multifunction Cells. . . . .. ....402

Thermophotovoltaic Cell . . . . . . . .

Multicolor Cells . . . . . .................403

Concentrator Systems . . . . . . . . . . . . . . . . . . . . 403

Photovoltaic Cogeneration .. ..............406

The Credibility of the Cost Goals . . . . . . . . . . . . 407

Markets . . . . . . . . . . . . . . . . . . . . . . . . . . .. ...408

An Analysis of Manufacturing Costs. .. ....412

Silicon. . . . . . . . . . . . . . . . . . . . . . . . ......412

Thin Films . . . . . . . ....................420

MaterialsAvailability and Toxicity. ... .......421

Silicon . . . . . . . . . . ......................422

Cadmium . ............................422

Gallium Arsenide. . .....................423

Performance of Cellsin Real Environments. ..423

PassiveCooling. . ......................424

ActiveCooling. . . ......................424

Photochemical EnergyConverslon. . ........425

LIST OF TABLES

Table

No. Page

l. a) Key Milestones for National Photovoltaic

Conversion Program; and b) Goals for

ConcentratorSystemsUsingSilicon Cells .394

2. PhotovoltaicCell Efficiencies . . . . . . . . ....398

3. Temperature Dependence of Photovoltaic

Devices . . . . . . . . . ......................407

4. Market Forecasts for Photovoltaic Devices

at Different Prices. . ....................410

Years To Achieve Indicated Price Reduction

as a Function of Learning Curve and

Assumed Growth in Demand . . . . . . .......412

The Distribution of Costs in the Manufacture

of Silicon Photovoltaic Devices Using

ContemporaryTechnology. . .............414

7. The MajorSt6psin Manufacturing a Silicon

Photovoltaic Device . . . . . . . ...:..... ....419

8. EffectiveConvective Heat-Transfer

Coefficients [ke

] for a Variety of Cooling

Systems . . . . . . . . ......................424

LIST OF FIGURES

Figure

Page

Array of Silicon Photovoltaic Cells

Providing PowertoPumpWater . ........393

A Typical Photovoltaic Device . . . . . . . . . . .396

An lnterdigitated BackContact SolarCell

and CrossSection. . ...................401

The Vertical MultijunctionCell . .........401

Thermophotovoltaic Converter . .........403

Experimental Concentrating Photovoltaic

Array in Operation. The Array Employs

Fresnel Lenses and Silicon Photovoltaic

Cells . . . . . . . . . . . .....................404

Breakeven Costs for Concentrating

PhotovoltaicCollectorsCompared WithFlatPlate Devices. .,..... . ................405

Historical Learning Curves From the

SemiconductorIndustry. . ..............409

PhotovoltaicArray Prices for Several Market

Projections. . . . . ......................411

Commercial Silicon Photovoltaic Cells ...413

Silicon Ribbon Being Grown by the ’’EdgeDefined Film-FedGrowth” Process .. ....417

Thin-Film Cadmium Sulfide-CopperSulfide

SolarCells . ..........................420

Photochemical Energy Conversion. .. ....425
Chapter X

Energy Conversion With Photovoltaics

INTRODUCTION

Photovo taic cells (often called “solar cells”) are semiconductor devices

which are capable of converting sunlight directly into electricity. Generating

electricity in this way has obvious advantages. The photovoltaic cells have no

moving parts, and they do not require high-temperature or high-pressure

fluids. Since they are extremely reliable, quiet, safe, and easy to operate, they

are ideally suited to onsite applications. Photovoltaic energy production is

unlimited by scarce materials, since cells can be manufactured from silicon,

one of the Earth’s most abundant elements.

There is no doubt as to the technical feasibility of generating electricity

from photovoltaic devices. The units have been used for many years in the

space program and to provide power in remote terrestrial sites. The array of

silicon cells shown in figure X-1 provides power to pump water in a remote

location in Arizona.

The most immediate barrier faced by all photovoltaic systems is the present high cost of the devices. Photovoltaic arrays could be purchased in large

quantities in late 1977 for about $11 per peak watt of output. * Electricity from

systems using such cells costs $1.50 to $2.00/kWh.

Figure X-1 .—Array of Silicon Photovoltaic Cells

Providing Power to Pump Water

.

SOURCE Solar Technology International

Development work to reduce the cost of

photovoltaic energy can be divided into

three general categories:

1. Reducing the cost of manufacturing the

single-crystal silicon celIs which are

now on the market;

2. Developing techniques for mass pro3

ducing and increasing the performance

of cells made from thin films of materials such as CdS/Cu2S or amorphous

silicon, and

Developing high-efficiency cells which

can be installed at the focus of magnifying optical systems,

It is technically possible to use any of

these approaches to reduce costs to $1 to $2

* Photovoltaic prices throughout this paper refer to

the sel I Ing price of arrays of cel Is encapsulated to protect them from the weather, f o b the manufacturing

facility In 1975 dollars The peak output of a cell

refers to the output which would be obtained If the

cell were exposed to the Sun at the zenith on a clear

day.

393
394 ● Solar Technology to Today’s Energy Needs

per peak watt (electricity costing $0.10 t o

$0.40/kWh) during the next 3 to 5 years. The

achievement of costs below $1 to $2 per

watt will require a considerable amount of

engineering development work. Progress in

any of a number of current research programs would give us considerably more confidence about the prospects for achieving

substantialIy lower costs.

A set of goals for reducing the cost of

silicon photovoltaic devices was established

somewhat arbitrarily during the crash Project Independence studies conducted in

1973. The Department of Energy (DOE) believes that, with some relatively minor adjustments, these goals are achievable and is

using them for planning purposes. The present goals are: $1 to $2 per watt by 1980-82,

$0. SO/watt by 1986, and $0.10 to $0.30/watt

by 1990. Current goals are shown in table

X-1. The lower cost goals appear to be optimistic but not impossible.

The DOE price goals assume that the arrays will last approximately 20 years. (Presently, terrestrial arrays are guaranteed for 1

year.) This seems to be an attainable objective, although more data is required on the

degradation rate for arrays exposed to the

environment for long periods of time. Silicon cells apparently fail only when the material used for encapsulation cracks or

leaks. Structural failures and corrosion have

occurred in improperly encapsulated devices, ’ and most clear plastics darken with

prolonged exposure to sunlight, cutting

down the light reaching the cells. Glass or

acrylic encapsulation should, however, be

able to prevent these problems.

‘A Johnson (M ITRE Corporation), private communication, 1977.

Table X-1

a) Key Milestones for National Photovoltaic Conversion Program

——

Array price in 1975, Production rate,

dollars per peak megawatts

peak watt per year

1. End of FY 1977 . . . . . . . . . . 11

2. End of FY 1978 . . . . . . . . . . 7

3. End of FY 1982 . . . . . . . . . . 1-2 20

4. End of FY 1986 . . . . . . . . . . 0.50 500

5. End of FY 1990 . . . . . . . . . . 0.1-0.3 50,000

SOURCE Photovoltaic program program summary January 1978, U S Department of Energy, Division of Solar Technology

b) Goals for Concentrator Systems Using Silicon Cells

Technical Commercial

feasibility* equipment* ●

1975 dollars Silicon 1975 dollars Silicon

per peak watt cell per peak watt celI

(entire system) efficiency (entire system) efficiency — —— —

1. End of FY 78. . . 2 16% 15 13.5%

2. End of FY 80. . . 1 180/0 2.75 16%

3. End of FY 82. , . 0.50 200/0 1.60 180/0

“ Laboratory proof of concept + reasonable estimate of cost of commercial system based on concept

“* F o.b. price of production technology.

SOURCE Annual Operation Plan, Systems DeflnltlonProlect (FY 1978), Sandla Laboratory
Ch. X Energy Conversion With Photovoltaics ● 3 9 5

PHOTOVOLTAIC CELLS

All photovoltaic installations will consist

of small, individual generating units — the

photovoltaic cell. Individual cells will probably range in size from a few millimeters to

a meter in linear dimension, A surprising

variety of such cells is available or is in advanced development since it has only been

in the past 5 years that serious attention has

been given to designing cells for use in anything other than spacecraft. Devices are

avaiIable with a large range of efficiencies

and voltages. Some cells are designed to

withstand high solar intensities and high

operating temperatures, while others are designed to minimize manufacturing costs.

The variety should not give the mistaken impression that this is an area where large

amounts of private or public research funding have been directed; indeed, many of the

projects described here are being conducted

by small research laboratories.

The photovoltaic equivalent of power

engineering is something of an anomaly in

the generating industry since it involves

manipulations in the miniature and silent

world of semiconductor physics instead of

steam tables, gears, and turbine blades. The

following discussion provides only a very

brief excursion through this complex field.

More complete discussions of the topics

covered can be found in several recent

publications .

2345 All that can be done here

is to outline some of the major effects influencing cell cost and performance.

The energy in light is transferred to electrons in a semiconductor material when a

light photon collides with an atom in the

material with enough energy to dislodge an

electron from a fixed position in the mater2t-i ). Hovel, Semiconductors and Semimeta/s,

Volume 11, Solar Cells, Academic Press, New York,

1975

‘C E Bacus, (ed ), Solar Cc//s, I E EE Press, New York,

1976

4 A Rothwarf and K W Boer, frog, in Solid State

Chem., 10(2), p 77 (1975)

‘K W Boer and A Rothwarf, Ann. Rev. Mat. Sci. (6),

p 303 (1976)

ial (i. e., from the valence band), giving it

enough energy to move freely in the

material (i. e., into the conduction band).

A vacant electron position or “hole” is

left behind at the site of this collision; such

“holes” can move if a neighboring electron

leaves its site to fill the former hole site. A

current is created if these pairs of electrons

and holes (which act as positive charges) are

separated by an intrinsic voltage in the cell

material,

Creating and controlling this intrinsic

voltage is the trick which has made semiconductor electronics possible. The most common technique for producing such a voltage

is to create an abrupt discontinuity in the

conductivity of the cell material (typically

silicon in contemporary solid-state components) by adding small amounts of impurities or “dopants” to the pure material.

This is called a “homojunction” cell. A typical homojunction device is shown in figure

x-2.

An intrinsic voltage can also be created

by joining two dissimilar semiconductor materials (such as CdS and CU2S), creating a

“heterojunction,” or by joining a semiconductor to a metal (e.g., amorphous silicon to

paladium) creating a “Schottky” barrie r

junction.

A fundamental limit on the performance

of all of these devices results from the fact

that (1) light photons lacking the energy required to lift electrons from the valence to

the conduction bands (the “band gap”

energy) cannot contribute to photovoltaic

current, and (2) the energy given to electrons

which exceeds the minimum excitation

threshold cannot be recovered as useful

electrical current. Most of the unrecovered

photon energy is dissipated by heating the

cell.

The bulk of the solar energy reaching the

Earth’s surface falls in the visible spectrum,

where photon energies vary from 1.8 eV

(deep red) to 3 eV (violet). In silicon, only
396 ● Solar Technology to Today’s Energy Needs

\

Rear Metal Contact

about 1.1 eV is required to produce a

photovoltaic electron, and in GaAs about

1.4 eV. Choosing a material with a higher

energy threshold results in capturing a larger

fraction of the energy in higher energy

photons but losing a larger fraction of lower

energy photons. The theoretical efficiency

peaks at about 1.5 eV, but the theoretical efficiency remains within 80 percent of this

maximum for materials with band gap

energies between 1 and 2.2 eV.6 7

‘M. Wolf, Energy Conversion, 11, 63(1 971 ).

‘Joseph J. Loferski, “Principles of Photovoltaic

Solar Energy Conversion,” 2Sth Artnua/ Proceedings,

Power Sources Conference, May 1972.

Electrons actually leave cells with

energies below the excitation voltage because of losses attributable to internal resistance and other effects, not all of which

are understood. a (An electron leaves a typical silicon cell with a useful energy of about

0.5 eV.)

The same kinds of fundamental limits apply to photochemical reactions in which a

light photon with energy above some fixed

‘M. Wolf, University of Pennsylvania, “Recent improvements and Investigations of Silicon Solar Cell

Efficiency, ” U.S./U.S.S.R. joint Solar Energy

Workshop, Ashkhabad, U. S. S. R., September 1977.
Ch. X Energy Conversion With Photovoltaics ● 397

excitation threshold is able to produce a

chemical reaction or a structural change

which can be assigned a fixed energy. T he

theoretical limit to the performance of several types of cell designs is shown in table

x-2.

The performance of real cells (also shown

in table X-2) falIs below the theoretical maximum for a number of reasons. One obvious

problem is reflection of light from the cell

surface (which can be reduced with special

coating and texturing) and reflection from

the electrical contacts on the front surface

of the cell (which can be reduced with careful contact design). ’ Losses also result from

the fact that the photo-generated electrons

and holes, which fail to reach the region in

the cell where they can be separated by the

intrinsic voltage, cannot contribute to

useful currents.

Photo-generated charges can be lost

because of imperfections in the cell crystal

structure, defects caused by impurities, surface effects, and other types of imperfections. Losses are minimized if a perfect crystal of a very pure semiconductor material is

used, but producing such a crystal can be extremely expensive. Manufacturing costs can

probably be greatly reduced if cells consisting of a number of smalI crystal “grains”

can be made to operate with acceptable efficiencies. The size of the grains which can

be tolerated depends on the light absorbing

properties of the cell material. If absorption

is high, photovoltaic electron-hole pairs will

be created close to the cell junction where

the voltages exist; relatively smalI grain

sizes can be tolerated since the charges

need drift only a short distance before being

sorted by the field.

Silicon is a relatively poor absorber of

light and, as a result, cells must be 50 to 200

microns thick to capture an acceptable fraction of the incident light. This places

rather rigorous standards on the sizes of

‘J Llndmayer and J F Allison, Cornsat Tech. #3 ,

1973, p 1

‘OJ R Hauser and P M Dunbar, IEEE Transactions

on E/ectron Devices, E D-24 (4), 1977, p 305

crystal grains which can be tolerated, and al I

commercial sit icon celIs are now manufactured from single crystals of silicon. It is

believed that if polycrystalline silicon is to

be used, individual crystal grains must be at

least 100 microns on a side if efficiencies as

high as 10 percent are to be achieved. 11 12 It

is important that the grains be oriented with

the grain boundaries perpendicular to the

celI junction so that charge carriers can

reach the junction without crossing a grain

boundary, A number of research projects

are underway to develop inexpensive techniques for growing such polycrystalline

material s

13 14 15 and for minimizing the impact of the grain boundaries. ” Efficiencies

as high as 6.7 percent have been reported

for vapor-deposited polycrystalline silicon

celIs with grains about 20 to 30 microns on a

side’ 7, and a proprietary process capable of

producing grains nearly a millimeter on a

side reportedly can be used to produce cells

with efficiencies as high as 14 percent,

Work is underway to improve crystal growing techniques and to enlarge grains with

lasers and electron beams.

Perhaps the most intriguing recent development is the discovery that an amorphous

silicon-hydrogen “alloy” can be used to con-

‘)A R Kirkpatrick, et al., Proceedings of the ERDA

Semiannual Photovoltaic Advanced Materials Program Review Meeting, Washington, D C , Mar 22-23,

1977

‘lA, Baghdad[, et al , ERDA Semiannual Photovolta ic Advanced Materla Is Program Review Meeting

‘ ‘T. L. Chu, et al., IEEE Transaction on Electron

Devices, ED-24 (4), 1977, pp. 442445.

14H. Fischer and W. Pschunder, (A EG-Telefunken),

“Low-Cost Solar Cells Based on Large-Area U nconventional Silicon, ” IEEE Transactions on E/ectron Devices,

ED-24(4), 1977, pp. 438-441

‘5L. D. Crossman, Research and Development of

Low-Cost Processes for Integrated Solar Arrays, (Third

quarterly progress report, ERDA EC (11-1 }2721,

Energy Research and Development Admlnistratlon,

Washington, DC., 1975), p. 38

“T H Distefano and J. J Cuomo, 1 BM, “Enhancement of Carrier Lifetime in Polycrystalllne Silicon, ”

Proceedings, National Workshop on Low-Cost Polycrystal I ine Silicon Solar Cel Is, Dallas, Tex , May 18-19,

1976.

“T. L Chu, et al., op. cit pp 442-445

‘“H` Fischer and W Pschunder, op clt , p 438
398 ● Solar Technology to Today’s Energy Needs

Table X-2.— Photovoltaic Cell Efficiencies —

1.

2.

3.

4.

5.

6.

7.

8.

9.

Performance

of commercial

cells

10-15

—

—

2-3

—

—

—

—

—

—

12.5

—

—

—

—

—

—

Reference

(1 ,2)

(4,5)

(6,7)

(8,9)

(lo)

(9)

(11 )

(12)

(1 ,13)

(3)

(14,15,16)

(17)

(18)

(19)

(20)

(21 )

(22)

● Techniques for reporting efficiencies differ Wherever Possible, efficiencies were chosen which assume air mass 1 and Include losses due to

reflection and contact shading

H. J. Hovel, Semiconductors and Semimetals, Vol. 2:

So/ar Cc//s (Academic Press, New York, 1975).

J. Lindmayer and C. Y. Wrigley, “Development of a 20

Percent Efficient Solar Cell,” (NSF-43090, National

Science Foundation, Washington, D. C., 1975),

J. V. DeBow, paper presented as part of the Proceedings of the Energy Research and Development

Administration Semiannual Photovoltaic Advanced

Materials Program Review Meeting, Washington,

D. C., Mar. 22-23, 1977.

1.1. Chu, S. S. Chu, K. Y. Duh, H. 1. Yoo, /EEE Transactions on Electron Devices, ED-24 (No. 4), 442 (1977).

H. Fischer and W. Pschunder (AEG-Teiefunken). “LowCost Solar Celis Based on Large-Area Unconventional Siiicon, ” IEEE Transactions on Electron

Devices. pp. 438-441.

D. E. Carlson, IEEE Transactions on Electron Devices,

ED-24 (No. 4) 449 (1977).

D. E. Carlson and C. R. Wronski, App/. Phys. Lett. 28,

671 (1976).

K. W. Boer and A. Rothwarf, Annu. Rev. Mater. Sci. 6,

303 (1976).

A. M. Barnett, J. D. Meakim, M. A. Rothwarf, “Progress

in the Development of High Efficiency Thin Film Cad10.

11.

12.

13.

14.

15.

16.

17.

mium Sulfide Solar Ceils,” (ERDA E (49-18)-2538,

Energy Research and Development Administration,

Washington, D.C. 1977).

G. A. Samara, paper presented as part of the Proceedings of the ERDA Semiannual Photovoltaic Advanced Materiais Program Review Meeting ,

Washington, D. C., Mar. 22-23, 1977.

J. 1. Shay, S. Wagner, H. M. Kasper, App/. Phys. Lett.

27,89 (1975).

L. J. Kazmerski, S. R. White, G. K. Morgan, ibid., 29,

268 (1976).

R. J. Stirn (Jet Propulsion Lab). “High Efficiency Thinfilm GaAs Soiar Cells”, 730-9 First Interim Report for

DOE/NASA, Dec 1977.

1. S. Napoli, G. A. Swartz, S. G. Liu, M. Klein, D. Fairbanks, D. Tames, RCA Rev. 38,76 (1977).

H. J. Hovel (IBM), “The Use of Novei Materiais and Devices for Sunlight Concentrating Systems,” Proceedings DOE Photovoltaic Concentrator Systems

Workshop, Tempe, ARiz., May 1977, pp. 35-54.

J. Gibbons (Stanford University), personal communication, October 1977.

M. D. Lambert and R. J. Schwarz, IEEE Transactions

on Electron Devices, ED-24 (No. 4), 337 (1977).
Ch. X Energy Conversion With Photovoltaics ● 399

Table X-2 references—continued

18.

19.

20.

R. M. Swanson and R. N, Bracewell, “Silico n

Photovoltaic Cells in Thermophotovoltaic Conversion” (EPRI ER-478, Electric Power Research institute, Palo Alto, Cal if., February 1977).

J. Harris, et. a/. (Rockwell International). “High Efficiency AIGaAs/GaAs Concentrator Solar Cells,” The

Conference Record of the Thirteenth /EEE

Pho fo vo/fa ic SpeciaIis ts Conference- 1978.

Washington, D. C., June 1978.

L. W. James and R. L. Moon (Varian Associates).

“GaAs Concentrator Solar Cells” The Conference

Record of the Eleventh IEEE Photovoltaic Specialists

Conference, Scottsdale, Ariz., May 1975, pp. 402-408.

struct photovoltaic cells with useful efficiencies. Efficiencies of 5.5 percent have

been measured” and 15 percent efficiency

may be possible. 20 The hydrogen apparently

attaches to “dangling” silicon bonds, minimizing the losses that wouId otherwise

result at these sites. Acceptable performance is possible, despite the large number of

remaining defects, because the amorphous

material is an extremely good absorber of

light; test cells are typically 1 micron or less

in thickness. 21 The properties of this complex material are not welI understood.

GaAs or CdS/Cu2S are also much better

absorbers of Iight than crystalline silicon, so

cells made from these materials can be thinner and tolerate smaller crystal grains than

was possible with the crystalIine siIicon.

Commercial CdS/Cu2S cells will probably be

6 to 30 microns thick, 22 23 and the crystal

structure produced with a relatively simple

spray or vapor deposit process is large

enough to prevent grain structure from significantly affecting celI performance.

The primary drawback of most of the

“thin film” celIs is their low efficiencies.

Research is proceeding rapidly in a number

“D E Carlson, RCA Laboratories, “Amorphous Silicon Solar Cells, ” IEEE Transactions on Electron

Devices, ED-24(4), 1977, pp 449-452

20 and C R Wronskl, App Phys, Lett. 28, 1976, p

671

2

‘A R Moore, E/ectron and Ho/e Drift Mobr’/ity in

Amosphous Si/icon (to be published)

22 Boer, op clt , p 319

2]) F jordan, Photon Power, Inc., El Paso, Tex ,

private communication, February 10, 1977

21.

22.

J. J. Loferski (Brown University), “Tandem Photovoltaic Solar Cells and Increased Solar Energy Conversion Efficiency,” The Conference Record of the

Twe/fth /EEE Photovo/taic Specialists Con/erence-1976, Baton Rouge, La., November 1976, pp.

957-961.

H. J. Hovel (IBM). “Novel Materials and Devices for

Sunlight Concentrating Systems,” /BM Journa/ of

Research and Development. Vol. 22, No. 2, Mar 1978,

T. T. Rule, et. a/. (Arizona State University). “The

Testing of Specially Designed Silicon Solar Cells

Under High Sunlight Illumination,” Twe/fth

IEEE- 1976. Pp. 744-750.

of areas, however, and a number of thin film

cells may be able to achieve efficiencies

greater than 10 percent.

Older designs of cadmium cells degraded

and failed relatively rapidly, but accelerated lifetime tests on modern designs appear to indicate that cells hermetically

sealed in glass with proper electrical loading

could have a useful life of decades. 24 25 26

Research is also underway on a number of

other materials which may be used to manufacture inexpensive thin film cells. Experimental cells have been constructed which

substitute iridium phosphide or copper inidium selenide for the copper sulfide in the

CdS/Cu2S heterojunction, and efficiencies

greater than 10 percent have been demonstrated in single-crystal laboratory cells

made with these materials. 2728

It is also possible to convert light energy

directly into electricity by exposing electrodes immersed in chemicals to sunlight. if

the materials are properly chosen, a current

can be produced without any net chemical

change in the materials used. Conversion efL

“J. Besson, et al , “Evaluation of CdS Solar Cells as

Future Contender for Large Scale E Iectriclty Production,” The Conference Record of the E/eventh /EEE

Plrotovo/taic Specialists Conference–1 975, Scottsdale, Ariz , May 6-8, 1975 (Institute of E Iectrlcal and

Electronics Engineers), pp 468-475

z 5E wcreenwichand F A Shlrland (Westinghous e

Research Labs), “Accelerated Life Performance Characteristics of Thin-Film CU2 5 Solar Cel/s-CdS, ” fro

ceedings, E Iectrochem Ica I Society Solar Energy Symposium, Washington, D C , May 2-7, 1976

“j F jordan, Photon Power,lnc , private com -

munication, Apr 5, 1976

27S Wagner, et al , Appl. Phys. Lett., 26, 229, 1975

“j Shay, et al , App/. Phys. Lett,, 27, 89,1975
400 . Solar Technology to Today’s Energy Needs

ficiencies greater than 5 percent have been

reported with polycrystalline CdSe-based

photoelectrochemical cells .

29 30 31 32 33 34

CELLS DESIGNED FOR USE IN

CONCENTRATED SUNLIGHT

High efficiencies are important for cells

used in concentrated sunlight, since increased cell performance means a reduction

in the area which must be covered with the

magnifying optical equipment, which dominates the system’s cost.

Modified silicon cells, designed to perform in concentrated sunlight are not inherently more expensive than ordinary cells,

but are always likely to cost more per unit of

cell area since production rates will be

lower and since more care will be taken in

their manufacture. However, since the cells

cover only a fraction of the receiving area,

much more can be spent on any individual

cell. Cells such as the thermophotovoltaic

device and the GaXAl1-XAs/GaAs cells may be

considerably more expensive per unit area

than the silicon devices, but this cost may

not be significant since the devices can be

used with concentrations of 500 to 1,000 or

more and can be much more efficient. A va -

riety of approaches are being investigated

for achieving high-efficiency performance in

concentrated sunlight.

Optimizing Conventional Silicon Cells for

Use in Concentrated Sunlight

The current from a photovoltaic cell increases almost Iinearly with increasing sunlight intensity and the voltage increases

slightly faster than the logarithm of the injgMark ‘j WrightOn, MIT, private communication,

Mar 26, 1977.

30A. B, Ellis, et al., ). Amer. Chern. Soc., 98, 1635,

6418, 6855(1 976)

“G. Hodes, et al , Nature, 216, 403,1976,

‘2B. Miller and A. Heller, Nature, 262, 680, 1976.

“D. L. Laser and A. ). Bard, j. E/ectrochem, Soc.,

123, 1027,1976.

“K. F Hardee and A j Bard, ), E/ectrochem. Soc.,

724, 215,1977

tensity. These effects would lead to an increase in overall cell efficiency, except that

the increased current densities in the cell

lead to increased resistive losses and other

effects. The design of standard silicon cells

can be optimized for operating in intense

sunlight by carefully designing the wires

used to draw current from the cells, optimizing the resistivity of the cell material, changing the thickness of the cell junction, and

otherwise taking pains in celI manufacture

(e.g., better antireflective coatings and surface texturing, higher quality silicon, precisely designed gridlines, etc.). Efficiencies

as high as 17.9 have been reported for silicon celIs operating at 1000 C in sunlight concentrated 200 times. 35

Several ingenious techniques have been

suggested for improving performance of siIicon devices used in intense sunlight with

novel designs.

Interdigitated Back-Contact Cells

An “interdigitated back-contact” cell exposes an unobstructed wafer of intrinsic

(i.e., very pure) silicon crystal directly to the

sunlight. The junctions that produce the cell

voltages, and that are attached to electrical

leads, are entirely on the back of the cell.

(The name comes from the shape of the positive and negative electrical contacts on the

back side of the cell. See figure X-3.) An efficiency of 15 percent concentration, with

ratios up to about 280, has been reported for

a preliminary version of this cell; it is believed that straightforward design improvements will result in cells which are at least

20-percent efficient. ”

15L s NapOil, et al,, RCA, “High Level concentration of Sunlight on Slllcon Solar Cel Is, ” RCA Review,

Vol 38, No 1, March 1977, p 91

16M D Larnmert and R. j Schwartz, pU rdue Un iversity, “The Interdlgitated Back Contact Solar Cell: A

Silicon Solar Cell for Use in Concentrated Sunlight, ”

/EEE Transactions on E/ectron Devices, ED-24(4), 1977,

pp 337-341,
Ch. X Energy Conversion With Photovoltaics 401

Figure X-3.— An lnterdigitated Back Contact

Solar Cell and Cross Section

I Hlgh-lifetlme bulk region I

SOURCE

Lammert M D and R J Schwartz “The Interdlgltated Back Contact

Solar Cell A Sll; con Solar Cell for Use (n Concentrated Sunllghl ”

IEEE Transacf/ons ori E/ecfron Dev/ces, VOI ED-24 (1977) p 337

Gallium-Arsenide Cells

Gallium arsenide has a higher theoretical

photovoltaic efficiency than silicon becaus e

its excitation threshold is better matched to

the energy in the Sun’s spectrum.

CaAs cells can be used to achieve high efficiencies in intense radiation, particularly if

they are covered with a layer of GaXA l1-XA s

which has the effect of reducing surface and

contact losses. Efficiencies as high as 24.5

percent have been measured for such

devices operating in sunlight concentrated

180 times, 38

In addition, both theory and experiment

show that the efficiency of GaAs cells is

reduced less by high temperature than is the

efficiency of siIicon celIs.

“H Hovel, op clt , p 195

“J Harris, et al , Rockwell International, “High Efficiency AI GaAs/G aAs Concentrator Solar Ce[ Is, ” The

Conference Record of the Thirteenth /EEE Photo

voltaic Specialists Conference-1978, Washington,

D C , June 1978

The Vertical Multifunction Cell

The edge-illuminated, vertical, multifunction cell shown in figure X-4 consists of a

stack of silicon homojunction devices qualitatively similar to standard cells, illuminated in such a way that the light enters the

cells parallel to the junctions. Several recent

calculations have indicated that these devices have the potential of achieving efficiencies as high as 30 percent, 39 although

very little work has been done on designing

and testing optimized cells. The maximum

measured efficiency to date is 9.6 percent

for a device without an antireflective

coating. 40

Figure X-4.—The Vertical Multifunction Cell

(edge illuminated)

I

incident sunlight

current

‘9H.J Hovel, IBM, “Novel Materials and Devices

for Sunllght Concentrating Systems, ” IBM journal of

Research and Development, 22(2), March 1978,

40T T Rule, et al , Arizona State University, “The

Testing of Specially Designed Silicon Solar Cells

Under High Sunlight Illumination, ” The Conference

Record of the Twelfth /EEE Photovo/taic Specialists

Conferenc&1976, Baton Rouge, La., November 1976,

pp 744-750.
402 ● Solar Technology to Today’s Energy Needs

The high potential efficiency results from

several features of the device:41 42 43

●

●

●

●

Since the vertical multifunction devices

are connected in series, they produce

higher voltages and lower currents than

other concentrator cells with the same

power output. The low currents reduce

the resistance losses. Series connections also mean, however, that considerable care must be taken to ensure

that all of the cell elements are illuminated since an unilluminated unit will

act Iike a large series resistance.

Like the interdigitated cell discussed

earlier, the vertical multifunction de

vices do not require contacts on the surface (the aluminum connections can

cover less than 1 percent of the surface

area)” and thus front surface reflections are minimized.

The multifunction device should be

able to make more efficient use of light

with relatively long and short wavelengths.

The multifunction devices should be

able to perform better than conventional silicon cells at high temperatures, and its performance at high temperatures improves in high light concentrations; the cells should, for example, be only half as sensitive to temperature at 1,000 x suns as they are in unconcentrated sunlight. 45

41B, L. Sater and C. Goradia, “The High Intensity

Solar Cell –Key to Low Cost Photovoltaic Power, ”

NASA Technical Memorandum ,NASA TM X-71718,

1975.

42C Goradia and B. L. Sater, “A First Order Theory

of the P-N-N Edge-1 Illuminated Silicon Solar Cell at

Very High Injection Levels,” IEEE Transactions on

Electron Devices, Vol. ED-24, 4, p. 342,1977,

“H. ), Hovel, IBM, “The Use of Novel Materials and

Devices for Solar Concentrating Systems,” Proceedings DOE Photovoltaic Concentrator Systems

Workshop, Scottsdale, Ariz., May 24-26,1977.

4 4

6. L. Sater, “Current Technology Status of the

Edge-illuminated Vertical Multifunction (VM)) Solar

Cell, ” November 1977 (unpublished),

45 Goradia and Sater, op. cit., p. 350.

The extra manufacturing steps required to

fabricate these devices will make them

somewhat more expensive than conventional silicon cells, but this difficulty would

be offset if the high efficiencies are realized.

Horizontal Multifunction Cells

There have also been proposals for using

horizontal multifunction devices using silicon or GaAs. It may be possible to design a

cell array capable of producing relatively

high voltages on a single chip, thereby reducing the cost of interconnecting devices

and reducing series resistance in connections. The inherent efficiencies of these

devices are approximately the same as conventional cells, but it may be easier to use

the approach to develop practical cells

which can more nearly approximate the

potential of the materials.46

Thermophotovoltaic Cell

The “thermophotovoltaic” cells shown in

figure X-5 may be able to achieve efficiencies as high as 30 to 50 percent by making an

end-run around the fundamental limits on

cell performance discussed earlier. This is

accomplished by shifting the spectrum of

light reaching the cell to a range where most

of the photons are close to the minimum excitation threshold for silicon cells. The Sun’s

energy is used to heat a thermal mass to

1,800 ‘C (the effective black body temperature of the Sun is about 5,7000 C). A large

fraction of the surface area of this mass

radiates energy to a silicon photovoltaic

device. (Reradiation to the environment can

occur only through the small aperture where

the sunlight enters. ) A highly reflective surface behind the photovoltaic cell reflects

unabsorbed photons back to the radiating

mass and their energy is thus preserved in

the system .47

“H. J. Hovel, IBM, “The Use of Novel Materials and

Devices for Solar Concentrating Systems,” op. cit., p.

38

“R. M. Swanson and R. N. Bracewell, Silicon

Photovo/taic Cells in Thermophotovo/taic Conversion,

EPRI ER-478, February 1977.
Ch. X Energy Conversion With Photovoltaics ● 403

Figure X-5.— Thermophotovoltaic Converter

CONCENTRATED SUNLIGHT

FROM PARABOLOID

Thermophotovoltalc

Converter

SOURCE

Swanson, R M and R N Bracewell (Stanford Umverslty) “Sll(con

Photovoltalc Cells In Therm ophotovoltalc Conversion” EPRI ER.

478 ~1977)

Multicolor Cells

Another approach to achieving high cell

efficiencies involves the use of a number of

different materials to form cells optimally

designed for different colors of light. There

are two basic approaches: (1) the use of

selective mirrors to separate colors and

direct them to different cells, and (2) the use

of a vertical stack of photovoltaic cells arranged so that upper layers absorb only high

energy (i.e. short wavelength) photons, allowing the remaining photons to reach lower

cell levels,48 Little experimental work has

been done on these devices, but theoretical

analysis has predicted that the light-filter

devices could achieve efficiencies as high as

46 percent if two separate cells are used and

52 percent if three cells are used. ” MuItiIayer cells using Ge, Si, GaAs, and other

materials with two or more layers may also

be able to achieve efficiencies above 40 percent. 50 An ingenious scheme for separating

colors has been recently proposed which

uses a series of dyes capable of absorbing

sunlight and reradiating the energy in a narrow frequency band matched to the band

gap of each of a series of cell junctions. s

’ 52

A considerable amount of development

work will be required to design practical

devices, however, and the ultimate cost of

fabricating the devices cannot be forecast

with any confidence.

48H. J Novel, IBM, “The Use of Novel Materials and

Devices for Solar Concentrating Systems, ” op cit., p

38

49N. S Alvi, et al., Arizona State University, “The

Potential for Increasing the Efficiency of Photovoltalc

Systems by Using Multiple Cell Concepts,” Twelfth

IEEE-7976, OP cit., pp. 948-956

50] ] Loferski, Brown University, “Tandem Photovoltalc Solar Cells and Increased Solar E nergy Conversion Efficiency, ” Twe/fth /EEE-1976, op clt , p p

957-961

“A Goetzberger and W Breubel, App/. Phys., 14,

1977, p 123.

52 The technique was originally suggested for use in

connection with scintil Iation counters in R L Carwln,

“The Design of Liquid Scintlllatlon Cells, ” Rev. Sci, inst. 23, 755 (1 952); and R L Garwin, “The CO I Iectlon of

Light From Scintillation Counters, ” Rev. SCI. Inst. 37,

1010 (1 960).

CONCENTRATOR SYSTEMS

The contribution of photovoltaic cell

costs to the overall cost of an installed photovoltaic system can be greatly reduced if

an optical system is used to concentrate

sunlight on the cell, even though cells designed for use in concentrators may cost

more per unit area of cell surface than flatplate cells. If such systems are used, problems of reducing cell fabrication costs are

replaced with problems of mechanical engineering. In most cases, the energy required

to manufacture a concentrator array is

many times lower than the energy required

to manufacture a flat-plate cell array with a

simiIar area.

The variety of concentrating collectors

which can be used with photovoltaic de-
404 ● Solar Technology to Today’s Energy Needs

vices is reviewed in chapter XII. PhotovoItaic devices can be attached to most types

of tracking systems with minimal modifications to the basic collector design. (A twoaxis tracking system using Fresnel lenses to

focus light on silicon cells is shown in figure

X-6. ) Attaching a photovoltaic device to a

concentrating collector can, however, present some unique design problems:

● One-axis tracking collectors are unable

to illuminate the entire receiver surface

during most of the day. Thus, only a

part of the receiver can actually be

covered by cells. In general, it is

necessary to connect photovoltaic devices in a receiver in series to achieve

acceptable system voltages. Nonilluminated photovoltaic devices have high

Figure X-6.—Experimental Concentrating Photovoltaic Array in Operation.

The Array Employs Fresnel Lenses and Silicon Photovoltaic Cells

SOURCE Sandia Laboratories, Albuquerque, N Mex., 1976.
Ch. X Energy Conversion With Photovoltaics . 405

resistance and the output of a string of

cells connected in series would be

greatly reduced if one element of the

string were shaded.

● It is desirable to maintain a relatively

uniform illumination on most cells to

maximize cell performance. This is difficult to accomplish with most collector designs. It is possible to design cells

capable of performing with acceptable

efficiencies in the i Illumination patterns

of specific CoIIector designs. This can

be done, for example, by modifying the

pattern of electric contacts on the front

surface of the cell, but the market for

such specialized cells would necessarily be limited.

It is difficult to compare the attractiveness of concentrating and nonconcentrating photovoltaic devices because of the

large number of variables involved; the only

completely satisfactory way of making such

a comparison is to conduct a complete Iifecycle cost analysis of competing systems

operating in realistic environments (such as

those reported elsewhere in this study). The

following formula, however, can be used to

obtain a crude estimate of the cost of a concentrating collector which would be competitive with a flat-plate device (assuming

that no credit can be given for the thermal

energy which can be produced from the concentration systems):

where the variables are defined as follows:

c c = allowed cost of the concentrating

collector, excluding the solar cells

($/m2

)

CfP = cost of fIat plate cell array ($/kW)

nfP = the efficiency of the f tat-plate array

r e = ratio of the efficiency of the concentrator photovoltaic system (including

losses in the collector optics) to the efficiency of the flat-plate array (including

packing factors)

rs = ratio of solar energy reaching cells in

the tracking collector to the sunlight

(direct and diffuse) reaching the flatplate collector

r C = ratio of the cost of the concentrating

cell ($/kW in one sun) to the cost of a

fIat-plate cell array

Ci = cost of installing the flat-plate collectors ($/m2

)

rl = ratio of cost of installing a concentrator to the cost of installing a flatplate device

C o=annual cost of maintaining the flatplate system (cleaning etc.) in $/m2 o f

colIector

r O = the ratio of the cost of maintaining

the concentrating collector to the cost

of maintaining a flat-plate system (per

m

2

)

k l= the effective cost of capital

cm ––the cost of flat-plate supporting

structures ($/m2

)

C,= concentration ratio of collector

This formula has been used to construct the

curves shown in figure x-7.

Figure X-7.— Breakeven Costs for Concentrating

Photovoltaic Collectors Compared With Flat. Plate

Devices

0.10 0.20 0.30 0.40

EFFICIENCY OF CELLS USED IN THE

CONCENTRATOR

(not including optical losses)
406 . Solar Technology to Today’s Energy Needs

Assuming that concentrating systems cost

so percent more than flat-plate arrays to install and three times as much to operate on

an annual basis, concentrator systems

would be competitive with $500/kW—15

percent efficient flat-plate arrays if the concentrating collector costs about $70/m2 a nd

concentrating cells are 20-percent efficient.

The concentrator could cost about $180/m

2

if concentrating cells are 40-percent efficient. (This example assumes that the optical efficiency of the concentrators is 80

percent and the concentration ratio is at

least 10 times the ratio between concentrator cell costs and the cost of fIat-plate arrays. ) The allowed cost of concentrators will

be considerably larger if there is a useful application for the thermal energy available

from an active cooling system.

PHOTOVOLTAIC

The analysis thus far has considered only

the electric output of collector systems, but

the attractiveness of photovoltaic devices

can be increased significantly if effective

use can be made of the thermal energy carried away by water pumped over the back

surfaces of collecting celIs. Such systems

are the photovoltaic analogs of cogeneration devices, and an analysis of the opportunities presented by such devices is

much the same as those conducted for conventional systems. I n both cases, the net efficiency of systems can only be understood

by examining the combined demands for

electricity and thermal energy in each proposed situation. There are clearly many

useful applications for the thermal energy

with temperatures in the 500 to 100‘C range

which can easily be extracted from most

photovoltaic cogeneration devices. About

23 to 28 percent of the primary energy consumed in the United States is used at temperatures below 108 oC.

53

53 Battelle Columbus Laboratories, Survey of the Applications of Solar Thermal Energy Systems to /ndustrial Process Heat.

While the cost of mounting cells on tracking collectors is clearly a major concern,

there is also cause for concern about the

cost of mounting flat-plate arrays. If array

prices fall below $300 to $500/kW, the cost

of supporting and installing the arrays could

begin to exceed the cost of the arrays

themselves.

General Electric has proposed a design

for a photovoltaic shingle which may be

able to substitute for a building roofing

material. If costs reach $100 to $300/kW, it

may also be economical to use photovoltaic

sheets as a part of a wall surface. I n most

locations in the United States, the output of

a collector mounted vertically on a south-,

east-, or west-facing walI is 40 to 60 percent

lower than the output of a collector fixed at

an optimum orientation.

COG EN ERATION

With photovoitaic systems, the critical

question is whether the electric-generating

efficiency which is lost because of operating

the cells at higher temperatures is compensated by the value of the thermal energy

produced. Cell performance degrade s

almost Iinearly with temperature at temperatures of interest primarily because of a

drop in the operating voltage of the cell (at

high temperatures, thermally excited electrons begin to dominate the electrical properties of the semiconductor device). This

temperature dependence is commonly expressed in the following form:

where n (T) is the efficiency of a cell at temperature T (expressed in “C) and ß is the temperature coefficient. The temperature coefficient (ß) measured for a number of different cells is illustrated in table X-3. It can

be shown in most cases that if a use for lowtemperature thermal energy exists, it is preferable to accept these losses of efficiency

and use the thermal output from celIs directIy rather than to maximize cell performance
Ch. X Energy Conversion With Photovoltaics ● 407

Table X-3.—Temperature Dependence of Photovoltaic Devices

Cell Base Concentrate ion ß= temperefficiency resistivity ratio ature coef -

Material at 28° C(% ) C rficient

Silicon . . . . . . .,

Silicon . . . . .

Silicon ., . . . . . . . .

Silicon . . . . . . . . .

Silicon . . . . . . . . .

GaAs . . . . . . . . . .

GaAs . . . . . . . . . .

GaAs . . . . . ., . . . .

CdS ., . . . . . . . .

10.4

11.8

12.4

12.2

11.8

17.0

19.2

18.5

7.8

0.1

0.3

0.3

2.0

10.0

1

1

40

1

1

1

100

1000

1

0.0035

0.0035

0.0032

0.0040

0.0046

0.0022

0.0023

0.0021

0.004-0.005

—

SOURCES Silicon cell data from Edward Burgess, Sandla Laboratories, private communication.

GaAs data from L James, Varlan private communication

CdS data from John Meakln, Institute of Energy Conversion, Unlverslty of Delaware (private communlcat{on)

and attempt to use a photovoltaic-powered

heat pump to produce thermal energy,

GaAs and other high-efficiency cells are

less affected by high temperature operation

than are silicon devices .54 A commercial

silicon cell operating with an efficiency of

12 percent at 270 C has an efficiency of only

8 percent if operated at 1000 oC

55

, while a

GaAs cell with an efficiency of 18.5 percent

at 280 C can operate with 16-percent effi54H j Hovel, IBM, Semiconductors and Sernirneta/s,

op cit , p 168

‘

SE L Burgess and J C Fossum, Sand ia

Laboratories, Albuquerque, “Performance of n + -p

Sillcon Solar Cells in Concentrated Sunlight, ” /EEE

Transactions on E/ectron Devices, E D-24(4), 1977, p.

436

Sandia cell

Sandia cell

Sandia cell

Commercial cell

Commercial cell

Varian

Varian

Varian

Univ. of Delaware

ciency at 1000 C and about 12-percent efficiency at 2000 oC.56 

It is possible to operate flat-plate collectors at elevated temperatures, but cogeneration will probably be easier to justify for

concentrating systems. Care must be taken

to cool concentrator cells even if waste heat

is not employed. If photovoltaic cogeneration proves to be attractive, concentrator

photovoltaic systems may continue to be

economically attractive even if the price

goals for fIat-plate arrays are achieved.

56L. James, Varian Corp , private communication,

1977,

THE CREDIBILITY OF THE COST GOALS

The most satisfactory technique for anticipating the future cost of photovottaic devices wouId be to anticipate future manufacturing techniques and develop a precise

cost estimate for each processing step; this

approach is taken in the next section. Unfortunately, the results of such analyses are

inconclusive since many future manufacturing processes capable of dramatic cost

reductions are based on techniques which

are now only laboratory procedures or

which anticipate progress in research. It is

possible, however, to make some estimates

of potential cost reduction by examining the

history of cost reductions achieved in simiIar types of manufacturing.
408 Solar Technology to Today’s Energy Needs

A common statistical technique for

analyzing the history of cost reductions is

called the “learning-curve” technique. 57

This technique attempts to correlate the

price of a product with the cumulative production experience of the industry manufacturing the product. In many cases, a rough

correlation appears to exist, although the

rate at which prices decrease varies greatly

from one industry to another. The rate of

“learning” is quantified by determining how

much the price decreases when the cumulative production volume doubles: if a doubling of accumulated volume results in a price

decrease of 10 percent, the system is said to

be on a “90-percent learning-curve;” if a

doubling of production volume results in a

price decrease of 30 percent, the system is

said to be on a “70-percent learn i rig-c urve.”

The most obvious place to look for a

historical analogy for predicting the price

reductions possible in photovoltaic devices

is the semiconductor industry which produces silicon devices using many of the

techniques now used to construct silicon

photovoltaic devices. The history of prices

in the transistor and silicon diode industries

is illustrated in figure X-8. The results are difficult to interpret since the price reductions

clearly do not follow a simple linear learning curve, but they do indicate that a learning curve of 70 percent is not impossible.

The analogy is far from perfect, of course,

since miniaturization techniques which

were used effectively to reduce the price of

semiconductor electronics cannot be used

in the manufacture of photovoltaic devices;

the size of photovoltaic devices used in flatplate arrays cannot be reduced since power

produced by a unit area of photovoltaic surface is limited by the intensity of sunlight on

the Earth’s surface. The learning-curve

method is probably valid for making crude

estimates of future cell prices since learning

curves of 70 to 90 percent have been observed for most products, even when miniaturization is not used in the manufacturing

process.

“Boston Consulting Group, Perspectives on Experience, 1971.

MARKETS

The learning curve cannot be used to estimate the rate at which prices will fall

without information about the size of the

market at each future price. Unlike most

other power sources, the demand for photovoltaic devices exists at a large range of

prices, since the equipment can provide

power in remote areas where conventional

alternatives are extremely expensive. The

unique features of the equipment may lead

to the discovery of markets for energy where

no market now exists. The large elasticity of

markets, coupled with the fact that individual installations can be very small, has allowed an evolutionary growth in sales and a

gradual reduction in cell prices,

The free-world market for cells at 1976

prices was about 380 kW58 of which about

280 kW were soId by U.S. manufacturers.

U.S. Government purchases during this

period were about 108 kW, of which about

50 kW were used in satellites.59 Major commercial markets have appeared in communications equipment (68 kW), corrosion protection for bridges, pipelines and like applications (28 kW), and aids to navigation

(20 kW).6O Sales during 1977 were expected

to be about twice 1976 levels.

Several market surveys for photovoltaic

equipment have been completed during the

past several years, and some of these are

summarized in table X-4. The considerable

differences in the forecasts reflect differing

judgments about the future cost of conventional energy and other forms of solar

energy, about the rate at which an industrial

infrastructure capable of supporting Iargescale production can be established, and

about the potential costs of support equipment (storage, controls, etc. ) and instalIa58BDM Corporation, Characterization of the Present

Worldwide Photovoltaics Power Systems Market, May

1977, p. 1-1.

S9 I ntertechnology Corporation, Photo vo/ta ;C power

Systems Market /identification and Analysis, Aug. 23,

1977.

‘“lntertechnology Corporation, op. cit.
Ch. X Energy Conversion With Photovoltaics ● 409

Figure X-8.— Boston Consulting Groups’ Learning Curve

SILICON TRANSISTORS

1954 1960 1963 1968

$100.00

0.1 1 10 100

Industry Total Accumulated Volume

(million units)

1955

SILICON DIODES

1959 1965 1968

3 10 100 1,000 10,000

Industry Total Accumulated Experience

(million units)
410 ● Solar Technology to Today’s Energy Needs

Table X-4.– Market Forecasts for Photovoltaic Devices at Different Prices

[in megawatts of annual sales]

—

Array prices in dollars per peak watt

Marketing study 10 3 1 0.5 0.1-0.3

1. BDM/FEA

DOD market . . . . . . 10

Worldwide commercial market . . . . . . 1.5

2. Intertechnology Corporation . . . . . ., . . 0.5

3. Motorola . . . . . . . . . . . . . 1.5

4. Texas Instruments. . . . . 0.4

5. RCA. . . . . . . . . . . . . 0.8

6. Westinghouse . . . . —

75 100 — —

20 70 100 —

13 126 270 —

20-30 — — —

2.6 30 100 20,000

13 200 2,000 100,000

— — 96,000

DOE planning, objectives . . 1.0 8 75 500 5,000

SOURCES ERDA brteflng on the “Photovoltalcs Program, ” Sept 9, 1977.

BDM Corporation, “Characterlstlcs of the Present Worldwide Photovoltalc Power Systems Market, ” May 1977, p

1.1

Irrtertechnology Corporation, “Photovoltaic Power Systems Market Identlflcatlon and Analyses, ’ Aug 23, 1977

BDM Corporation, DOD Phofovo/tam Energy Conversion Systems Market /nventory and Ana/ys/s, Summary

Volume, p 17.

P D Maycock and G F Wakefield (Texas Instruments) “Business Analysis of Solar Photovoltatc Energy Conversion, ” The Conference Record of the E/evenfh /EEE P/rotovo/fam Specla//sfs Conference. 1975 Scottsdale, Arlz

May 1975, pp 252.255

The Motorola Corporation

tion. Some manufacturers, for example,

have been skeptical about the high forecasts

for small remote applications since many of

these applications require a considerable

amount of expensive marketing and engineering.

The surveys seem to agree that a significant fraction of sales during the next few

years will occur in developing countries.

Photovoltaic equipment is ideally suited to

places where no utility grid is available and

where labor for installing the equipment is

relatively inexpensive. Consumers in the

capital cities of many developing nations

now pay as much as $0.20 to $0.25/kWh for

electricity, and prices in more remote areas

are often higher (if power is available at

alI). 61 The modular nature of photovoltaic

“Telegrams received from A I.D from posts in

numerous developing nations during July and August

1977 [n response to a request for information about

local utlilty rates

equipment has the additional advantage of

allowing functioning power sources to be installed quickly and in sizes appropriate for

each application. Moreover, an investment

in the photovoltaic power source does not

commit a nation to finding a reliable source

of fuel or to maintaining a highly trained

group of operators—two serious problems

for developing countries,

Other possible areas where sales of photovoltaic equipment may increase rapidly during the next few years include applications

by the U.S. Department of Defense (large,

cost-effective purchases appear possible

during the next few years)62 and the armed

forces of other nations; the agricultural sector, for irrigation and other pumping ap-

‘2BDM Corporation, DOD Photovoltalc Energy Cor--

version S ysterns Market /nventory and A na/ys IS, 5ummary Volume, p. 17
Ch. X Energy Conversion With Photovoltaics ● 411

placations; and the transportation industry,

for highway markers and lighting. 63 64

If prices fall below about $0.50/watt, an

explosive growth in sales could occur since

at this price photovoltaic equipment might

provide electricity which is competitive with

residential and commercial electricity rates

in many parts of the United States. 65 66 B y

the time prices fall to $0.10 to $0.30/kW, the

photovoltaic electricity may be competitive

with electricity sold at buIk rates to large industrial consumers. Estimating sales at these

levels is extremely speculative since generating large amounts of power from photovoltaic devices would require a fundamental change in the ways in which the Nation

now supplies and consumes electric energy.

Moreover, when array prices reach these low

levels, the overall cost and attractiveness of

photovoltaic systems are likely to be dominated by factors other than the cost of the

celIs themselves. Before turning to an analysis of integrated systems, however, it will

be useful to examine the costs and capabilities of the assortment of photovoltaic devices which are or may be available in the

near future.

Each of the projections of markets can be

used to predict the rate at which prices fall

given an assumed rate of “learning.” Three

forecasts and three different learning curves

have been used to construct the forecasts

shown in figure X-9. It can be seen that with

the RCA estimate of markets and a 70-percent learning curve, the technique predicts

that prices will reach $500/kW in 1986. If

prices fall according to a 75-percent learning curve, however, the price will not reach

$500/kW until after 1990. Using the less optimistic Texas Instruments (Tl) estimates of

markets, prices would not fall to $1,000/kW

untiI nearly 1990, even with the 70-percent

learning curve,

‘‘Intertechnology Corporation, op. cit.

64BDM Corporation, Photovo/taic Market, op cit.

“Westinghouse Corporation, Fina/ Report: Conceptual Design and Systems Ana/ysis of Photovo/taic

Power Systems, Vo/ume /, Executive Summary, April

1977, p 45

“See volume I I of this study

Figure X-9. -Photovoltaic Array Prices for

Several Market Projections

NOTE: With the exceptfon Of the “DOD sales” curves, It has been assumed

that the Federal Government spends $129 ml Illon for photovoltalc systems

between 1978 and 1981, of which 40 percent IS actually used to purchase

cell arrays (the remainder being spent for des Ign, i nstallatlon, storage, control systems, and other supporting devices) The forecasts assume that

cumulatwe production of cel Is through 1975 was 500 kW and that average

array prices at the end of 1975 were $15/Watt

The figure also illustrates the extreme sensitivity of the forecast of potential price reductions to the assumptions made about intermediate markets. If the BDM Corporation

forecasts of potential cost-effective military

applications are correct and the militar y

purchases devices for all cost-effective applications, prices can fall to $500/kW by

1986, even if a 75-percent learning curve i s

assumed.

If the cost of photovoltaic devices is to be

reduced through an expansion of the market, the industry will have to grow extremely

rapidly for the cost goals to be met. For example, if prices follow a 70-percent learning

curve, the cost goals can be met if the pro-
472 ● Solar Technology to Today’s Energy Needs

duction rate of cells doubles each year. (The

times required to achieve different price reductions, given a learning curve and production doubling time, are summarized in table

X-5.) Such expansions are possible but they

could make it difficult for small companies

now manufacturing cells to expand fast

enough to meet demands.

[n spite of its limitations, the learningcurve technique can provide some useful

guidance by establishing whether the cost

goals anticipated for photovoltaic devices

exceed any historic rates (the goals are optimistic, but not impossible by this test), and

they can be used to explore the sensitivity of

price reductions to different forecasts of

potential markets.

AN ANALYSIS OF

MANUFACTURING COSTS

Silicon

The vast majority of the photovoltaic

celIs now being sold are single-crystal siIicon

cells in fIat arrays. (See figure X-1 O.) The bulk

of Federal funding to reduce the cost of

cells is being directed to silicon technology.

The Federal Low-Cost Silicon Solar Array

(LSSA) project, managed by the Jet Propulsion Laboratory (jPL) has made a careful

analysis of the component costs of each

step in the manufacturing process and is

Table X-5.— Years To Achieve Indicated Price Reduction as a Function of

Learning Curve and Assumed Growth in Demand

——

Learning Number of times production rates

Price reduction curve double each year

(PO

/ P) (percent) 4 2 1 1/2

70 3.0 5.5 10.0 18.0

30 75 3.6 6.6 12.3 22.6

80 4.4 8.4 15.7 29.4

70 3.4 6.2 11.4 20.9

50 75 4.0 7.5 14.1 26.1

80 5.0 9.5 18.0 34.0

70 3.8 7.2 13.4 24.7

100 75 4.6 8.7 16.5 30.9

80 5.8 11.0 21.1 40.2

70 4.1 7.8 14.5 27.0

150 75 5.0 9.4 17.9 33.7

80 6.2 11.9 22.9 43.8

Assumptions: Price in 1976 = PO = $15,000/kWea

Cumulative sales volume in 1976 = So = 500 kweb

Annual sales in 1976 = B = 250 (kWe)e

= to = 1976 (base date)

aJ w, yerk~.s, (.ARc(_J solar, lnC ) Pr!vatf? Communtd(on

bJ Llndmeyer, (Solarex Corp ) Private Comrnunlcatlon.

CA Cllfford, (Solarex Corp ) Private Communlcatlon. Oct 1976

SOURCE” Prepared by OTA
`Ch. X Energy Conversion With Photovoltaics ● 413

Figure X-10.— Commercial Silicon Photovoltaic Cells

Silicon Concentrator Photovoltaic Cells Commercial Silicon Photovoltaic Cells

Manufacturer:

1. Solarex.

2. Arco Solar (Printed contacts)

3. Motorola.

4, Optical Coatings Laboratory, Inc.

(Space Cell Utilized In Sat elites)

systematicalIy examining techniques for

reducing costs in four major areas.

●

●

●

●

Production of the pure silicon feedstock,

Preparation of a thin sheet of silicon,

Fabrication of cells, and

Arrangement of the cells in a weatherproof array.

JPL objectives for cost reductions in each

area are shown in table X-6. I n reaching

these goals, maintaining high cell efficiency

wilI be criticalIy important since many costs

in cell manufacture and in the instalIation

of photovoltaic arrays are proportional to

overalI celI area and not to power.

SILICON PURIFICATION

The purified polycrystalline silicon used

as the raw material of commercial cell

manufacture now costs about $65/kg. T h e

jet Propulsion Laboratory estimated that, if

the goal of $0.50/watt is to be reached, the

silicon material cost must be reduced to

Scale in Centimeters Photos John Furber, OTA

Manufacturer:

1-4. Spectrolab.

5. Sandia Laboratories,

6. Solarex.

about $1 O/kg and the amount of siIicon

wasted in the manufacturing process considerably reduced. b

’ Perhaps even more importantly, current techniques for manufacturing silicon are extremely inefficient in

their use of energy; approximately 7,000

kWh of energy is required to manufacture a

cell with a peak output of 1kW (assuming

that celIs are 100 microns thick and 82 percent of the silicon entering the manufacturing process is wasted). 68 This means that the

device must operate in an average climate

for about 4 years before it produces as much

energy as was consumed in manufacturing

the component silicon.

Several promising techniques for improving the purification have been experimentally verified, and it should be possible to

‘7H Macomber, j PL, Proceedings, ERDA Sernia nnua / Solar Photo vo/ta ic Program Review Meeting,

Silicon Technology Programs Branch, San Diego,

Calif , January 1977, p 68.

“L P Hunt, Dow Corning Corp , “Total Energy Use

In the Production of S i I icon Solar Cel Is From Raw

Materials to Finished Product, ” Twe/fth IEEE-1976, op.

cit `, pp 347-352
414 ● Solar Technology to Today’s Energy Needs

Table X-6.—The Distribution of CoStS in the Manufacture of silicon Photovoltaic Devices

Using Contemporary Technology [aii costs in $/peak W]

Ingot technology

Non ingot

technology

Representative

data for 1976 1978 1980 1982 1984 1986

Polysilicon . . . . . . . . . 2.01 1.16 .76 .28 .14 .06

Crystal growth and

cutting . . . . . 4.18 2.50 1.43 .67 .23 .10

Cell fabrication . . . . . . . 5.97 1.87 1.01 .58 .34 .19

Encapsulation

materials . . . . .78 .22 .12 .09 .07 .03

Module assembly and

encapsulating . 3.99 1.25 .68 .38 .22 .12

Price . 16.96

Goal . . . . . . . . . . 20.00 7,00 4.00 2.00 1.00 50 ——

‘Does not Include Inflation— prices In 1975 constant dollars

NOTE The detailed price goal allocations are for slllcon Ingot technology up through 1982 and for slllcon sheet Technology In 1984 dnd 1986 These

al local Ions for use w It h In the LSSA Pro)ec I are subject to rev IS Ion ds better knowledge Is gal ned and s ho[) Id not be ( onstr ued as

predicted prices

I t Is ex pec ted t hal after 1982, Ingot and sheet lec h ndogy mod u Ies w I I I be cost corn pet I t I ve, w I t h the poss I btl I t y that the $ 50/W goal ~ an be

achieved by e It her technology Technology developments and future product I on c OS! parameters w I I 1 be malor factors I n determ I n I nq t hc~ most

cost effective deslg ns

SOURCE Jet Propulslorl Laboratory Low Cost SIIIC on Solar Array Pro)e( t Recel~ed by OTA June 1977

develop cell arrays capable of producing all

the energy used in their manufacture in 3 to

4 months. ” A significant amount of chemical engineering and process development is

needed, however, to demonstrate that these

laboratory experiments can be scaled-up by

many orders of magnitude to form the basis

of a commercial faciltiy.

It is possible to produce photovoltaic

celIs with siIicon less pure than the “semiconductor grade” material now used in cell

manufacture, but a careful analysis must be

made to determine whether the lower silicon costs would compensate for the additional system costs which would be incurred

by the reduced cell efficiency which results.

Manufacturing very high efficiency cells for

use in concentrators may even require silicon which is of higher purity than the materiaI now used to produce most semiconductors.

Silicon costs probably represent the single

greatest technical barrier to meeting JPL’s

cost goals for nonconcentrating arrays in the

early 1980’s. This is because construction of

b9Hunt, Ibid,

plants capable of manufacturing silicon in

quantities large enough to achieve the required cost reductions would need to be

established very quickly— probably within

the next year — and the investments required

will be large, compared to previous spending in photovoltaic manufacturing New silicon plants are Iikely to require more capital

investment per unit of cell production than

any other stage in the celI production process — between $20 miIIion and $40 miIIion

for a single plant. There is no incentive to invest in such equipment of this magnitude

solely for the purpose of selIing sit icon to

the semiconductor industry because material costs for these devices are already a

small part of the device cost. Silicon prices,

therefore, are unlikely to fall by 1982 unless

the Government takes some action.

Improved sawing techniques may be able

to cut silicon material requirements by twothirds by producing thinner silicon cells and

reducing the material lost as sawdust. 70 Im-

‘

(

’A Kran, I HM, Proceeding, S yn?po~lun? on t h e

M,] ter/a/s .$cience$ Aspect of Thin / //n? $y~ tern~ for

So/ar F rwrgy Con\ wsion, Tuscon, Arlz , Mdy 20-22,

1074
Ch. X Energy Conversion With Photovoltaics ● 475

proving the techniques used to grow crystals

could also reduce losses. Development of a

ribbon or thin-film, crystal-growing process

could greatly reduce wastage. Development

of an amorphous silicon cell with adequate

performance would dramaticalIy reduce silicon requirements in cells since these cells

would probably require less than I percent

of the silicon used in commercial cells, Silicon requirements can also be greatly reduced if concentrator devices are used.

FORMATION OF SILICON SHEETS

Growing pure silicon crystals and sawing

them into thin waters now represents about

25 percent of the price of arrays. 7’ A number

of active programs exist for improving the

batch processes in which crystal ingots are

currently being produced and sawed into

wafers 72 techniques have also been designed for drawing single-crystal sheets or

ribbons directly from molten siIicon, but a

considerable amount of engineering work

must be done before a commerciaI process

if available. Development of an Ingot technique adequate to meet the $1 to $2 per

watt cost goal appears to be assured, and

improved ingot techniques may even be

adequate to meet the 1986 cost goal. The

problems remainlng in this technology appear to be largely ones of improving mechanical designs, this is another area where

the program could be accelerated by the

Government Although crystal growing

equipment IS relatively expensive, unsubsidlzed commercial Interest in this kind of

equipment In the next few years is Iikely to

be greater than commercial interest in advanced silicon refinement processes. Research progress which makes it possible to

use polycrystalIine or amorphous materials

wouId substantialIy reduce the cost of this

step In production

——.—— —

7‘“ Low-(’ost SI I IC on Sol at Array Pro]ect, ” Qudrter)y

Report-l, J Uly-september 1976, pp 1-4

“jet propulylon Ldbordtory, Low-cost $//icon .$o/dr

Array F’ro/ect, Report-J, July- September 1976, pp

4-57

7

‘M~comber, ] P1 , op c It , p 71

Crystal Growing and S/icing

Ali of the silicon photovoltaic devices

now sold are manufactured from wafers

sawn from single-crystal boules (2- to 3-inch

diameter cylinders of silicon). These wafers

represented about 35 percent of the cost of

photovoltaic arrays in 1976 (see table X-6)

The crystals are commonly grown by dip

ping a seed crystal into a silicon melt in a

quartz crucible which is a few degrees

above silicon’s melting point and by slowly

withdrawing the growing cyrstal from the

melt. The crucible and the crystal are

counter-rotated to grow a straight crystal of

uniform, circular cross-section The crystal

is pulled from the crucible until most of the

molten silicon has been withdrawn and

removed from the melt. The entire apparatus is then aIlowed to cool so that the

crystal can be taken out of the airtight

chamber, As the remaining molten silicon

solidifies in the crucible, the crucible usually breaks, adding about $50 to the cost of

the boule This procedure is called the

“Czochralskl ” (Cz) or “Teal-Little” method.

The boule is sawed into thin wafers which

are sent to the next stage of the cell fabrication process. Several commercial silicon

celIs manufactured using this technique are

shown in figure X-10. A variety of new concepts have been proposed for reducing the

cost of the crystal-growlng processes, some

Involve radicalIy new approaches where thin

tilms or ribbons are solifified directly from

the molten silicon.

• I reproved sawing techniques might re

duce the material lost in the sawing

process; currently, nearly 50 percent of

the crystal grown is lost as silico n

sawdust. ” Techniques are being developed which use muItiple saws wIth thin

saw blades, sawing wires, and other advanced processes to decrease the material lost In sawing and increase the

number of silicon wafers produced

from a single crystal by producing thinner wafers. 74 75

“Texas Instruments, I nc , and L’drlan have F RDA

contrdcts to Improve sawl ng technlquej See R G

Forney, et al J PL, op clt

7’LSSA Quarter/v Report, op clt , pp 4-117, 4-115
416 ● Solar Technology to Today’s Energy Needs

The molten silicon in the quartz crucible from which the crystal boule is withdrawn can be continuously replenished,

leading to longer crystal draws and a

lower requirement for crucibles. (This

process could also save a number of

processing steps.)

The silicon material lost in sawing

could be recycled for further use if it is

not contaminated in the cutting process.

Techniques can be used to increase the

diameter of the crystals grown by using

the standard Czochralski process. Crystals now in use are typically 3 inches in

diameter, but crystals 10 inches in

diameter have been grown in laboratories . An experiment is now underway to grow three 12-inch diameter

crystals in one continuous heating cycle. 77 Choice of an optimum diameter

will depend on a detailed study of the

manufacturing process. (Problems in

cutting the crystals increase with

crystal diameter. )

The rate of crystal growth can be increased if columnar grains can be tolerated in cell wafers (research is required

to determine the extent to which such

grains can be tolerated or their effects

minimized).

Considerable energy and capital equipment could be saved if a process could

be developed for growing a crystal in a

mold. The Crystal Systems Company is

currently examining a concept in which

a seed crystal is placed in one end of an

insulated mold filled with molten silicon. A temperature gradient is maintained along the mold so that the crystal grows from the end with the seed

crystal to fiII the mold. 78 This technique

is commonly used to grow metal crystals, but has not yet been successfully

“M. GoIdes (President of SunWind Ltd ), private

communlcatlon, Aug 16, 1976

“R G Forney, et al , j PL, op clt

7 8R C Forney, et al , jPL, op cit.

adapted to the growth of semiconductor-grade silicon crystals.

improvements in cutting circular

wafers into the hexagons required for

close packing are possible through the

use of a Iaser-slicing technique being

developed by Texas Instruments.

Table X-6 indicates that if current techniques are converted to mass production,

silicon wafer blanks can be produced for

about $112/m2 ($0.80/watt if the cell is 14-

percent efficient) if polycrystalline material

were purchased for $35/kg. This could be

reduced to approximately $78/m2 if polycrystal Iine material were purchased for

$10/kg. A recent analysis conducted for

DOE by Texas Instruments estimated that it

would be possible to produce “solar-grade”

polycrystalline silicon for $10/kg (o r

$214/kW at 14 percent efficiency), 79 and for

approximately $5/kg if arrays are to be

manufactured for $1 ()()/k W. 80

Single Crystal Growth—Ribbons and Sheets

Research has been underway for at least

15 years to develop a process by which

single-crystal silicon can be produced in the

form of ribbons or sheets. Thin ribbons

would be appropriate for use in solar cells

without the crystal-slicing steps required for

boules. This would eliminate the costs involved in slicing the crystals and could

make more efficient use of silicon. This

wouId not only eliminate expensive operating steps, but could reduce trimming

losses when cutting round cells to hexagonal

cells. The Department of Energy has been

funding Mobil-Tyco, Solar Energy Corp.,

IBM, Motorola, RCA, the University of

South Carolina, and Westinghouse to assess

the merits of a variety of processes for growing single-crystal ribbons and sheets. 81

One technique for doing this is the “edgedefined, film-fed growth” process (EFG);

“Ibid.

‘“lbld

a’ E RDA, Semiannua/ Nationa/ Yo/ar Photovo/tage

Program Review Meeting, University of Maine, August

1976
Ch. X Energy Conversion With Photovoltaics . 417

work began on this process about a decade

ago. The EFG process utilizes a graphite die

on top of a crucible of molten silicon. A narrow pool of molten silicon forms on the top

of the die by capillary action. A thin ribbon

of silicon is slowly withdrawn from this

pool. 82 Such a ribbon is shown in the growth

82B Chalmers, “The Photovoltaic Ceneratlon o f

E Iectrlcity,” Scientific American, November 1976, p

34

process in figure X-11. Photovoltaic cells

made from EFG ribbons have shown efficiencies as high as 10 percent.

83 Intensive

work is proceeding on the EFC process but

several difficulties remain: 1 ) contain i nation

‘~K, Ravi, et al., 12th IEEE Photovoltaic Specialists

Conference, Baton Rouge, La., Nov. 15,1976

Figure X-1 1 .—Silicon Ribbon Being Grown by the “Edge-Defined Film. Fed Growth” Process

(Mobil Tyco Solar Energy Corp )
478 Solar Technology to Today’s Energy Needs

of the

results

siIicon

by the

ribbon by impurities from the die

in efficiencies lower than other

cells; 2) the graphite die is attacked

molten silicon; and 3) the process is

currently quite slow. Ribbons 2- to 21A-cm

wide can now be grown at rates of 2 to 7 cm

per minute. The objective is a growth rate of

approximately 18 cm. per minute. a

’ A recent

analysis by IBM indicated that a largediameter Czochralski boule can grow silicon

crystal areas at a rate equivalent to 20 to 40

simultaneously pulled ribbons .85

Other ribbon techniques under investigation include the IBM “Capillary Action

Shaping Technique” (CAST) which uses a

wetted die, and the RCA “inverted stepanov” technique which uses a nonwetted die.

Both techniques share many of the problems of the EFG approach. a

’

Another process for manufacturing ribbons is the web-dendrite crystal growth

process. Unlike EFG, this process requires no

die, and the die contamination and die erosion problems are, therefore, avoided. Strips

of silicon 2 meters long, 0.15mm thick, and

22mm wide have been grown at rates of 2 to

3 cm per minute; the objective is a growth

rate of 18 cm per minute.

87 Difficultie s

which remain with this process include: 1)

the fact that careful temperature control is

necessary, which probably precludes the simultaneous growth of several ribbons from

one melt; and 2) relatively slow growth rates.

Polycrystalline Sheets

Work is also underway to develop lowcost techniques for producing sheets of

polycrystalline silicon with crystal grains

large enough in size and oriented properly

“lbld

“ 5

A Kran (1 BM), “Single-Sillcon Crystal Growth by

Czochralski and Ribbon Techniques–A Comparison

of C a pa bl I I t Ies, ” Proceedings, S yrnpos I urn on the

Material Sciences Aspect of Thin Film Systems for

So/ar [nergy Conversion, Tuscon, Ariz , May 20-22,

1974, Pp 422-430

“’’Low-Cost Silicon Solar Array Project, ” Quarterly

Report-1, july-September 1976, p 4-57

“lbld

to allow the production of cells with acceptable efficiencies. Some processes are yielding individual crystal grains 1 to 10 mm on a

side, blurring the distinction between single

and polycrystalline devices. Perfection of

such processes could lead to more efficient

use of the silicon feedstock and replaces the

expensive task of growing a perfect crystal

with a casting, forming, or depositing process which may be much less expensive.

Some of the methods proposed would create a thin layer of polycrystalline material

on a solid backing, or substrate, thus

eliminating the cost and material waste

associated with slicing the silicon material

into wafers. Concepts include:

1. Dipping a substrate into molten silicon,

covering the substrate with a thin

coating of polycrystalline siIicon.

(Honeywell).

2. Continuously pulling a thin sheet of sili3

4

5

con from the surface of a pool of

molten metal where silicon vapor is being deposited. (General EIectric).

Depositing silicon from a silicon-halide

gas directly onto a hot substrate. It may

be possible to combine the final stage

of silicon purification (distillation) with

this deposition process (Rockwell international and Southern Methodist University).

Forming heated silicon material under

pressure in rollers (University of Pennsylvania).

Casting blocks o f poiycrystalIine

material and slicing the blocks (Crystal

Systems, Salem, Mass.).

CELL FABRICATION

The process of converting silicon wafers

into an operating photovoltaic array with 1

kW peak output involves a number of individual steps which now require many hours

of hand labor,88 adding about $6 to the price

‘

8P D. Maycock and G F Wakefleld, Texas instruments, “Business Analysls of Solar Photovoltalc

Energy Conversion, ” Eleventh IEEE-7975, pp 252-255
Ch. X Energy Conversion With Photovoltaics . 479

of a 1 watt cell. Processes include the creation of the photovoltaic junction, the addition of electrical contacts, and the application of anti-reflective coatings. 89 Studies of

mass-production techniques conducted for

JPL by Motorola, Texas Instruments, and

RCA all indicate that this cost could be

reduced to $0.30 to $0.90/watt90 using

known mass-production apparatus, if plants

capable of producing about 5 to 50 MW annualIy were constructed. The costs associated with each step in the fabricating

process are shown in table X-7. Projecting

further price reductions, however, requires a

fair amount of optimism. It can be seen

from table X-4, however, that cell prices

must fall to $1 to $2/watt before there will

be markets large enough to support several

competing fabricating plants of the size envisioned in the JPL studies. It is likely that

manufacturers wilI show greater desire to invest in fabrication equipment

more capital-intensive devices

————

“’F RDA “ Photovol talcs Program “

‘

(

’h! acomber, J []l., op clt , pp 71-72

than in the

required to

manufacture silicon wafers. This is because

significant cost reductions can be ac -

complished with plants much smaller than

50 MW/year, and it is much less likely that

fabricating plants would become obsolete–even if breakthroughs dramatically

reduce the cost of manufacturing silicon

wafers.

The laborious and expensive processes for

making photovoltaic celIs are also extremely inefficient in their use of energy. Silicon

material, for example, is melted when it is

purified, cooled, and shipped to the crystalgrowi ng facility where it must be melted

again to grow a crystal, again cooled,

heated at least once more during cell fabrication, and then cooled to ambient temperatures for the third time. No attempt is

made to recover any of the heat wasted

when the cells are cooled. The efficiency of

this process could clearly be improved

significantly to reduce both the cost of the

cell and the time required for the cell to

“pay-back” the energy used in its manufacture once it is installed.

Table X-7 . —The Major Steps in Manufacturing a Silicon Photovoltaic Device

—

Surface Junction Other Module

prep format ion Metalization processes fabrication Totals

(alternate)

—.— -.——

Motorol a 0.282 0.080 0.082 0.042 0.385 0871

R C A 0.003 Ion 0.044 0.101 0,045 0.114 0309

(Spin 0.081 )

& PO CI3

to

0.343

(Print 0.048)

Texas Instru -

ments 0.035 Spin 0.048 Thik Film 0.050 0.093 Hermetic 0.272

(Ion O 092)

0391

Nonhermetic 0135 to

0.586

ASSumptions

I) cells would be made uslnq wafers Sliced from ingots

2) Based upon an extrapolation of present technology with reasonable development but wlthout technological breakthroughs

3) 50 MW/year productlon of a slngle deslgn.

4) 14 percent cell efficiency

‘ Does not Include cost of sllicln material nor wafers

SOURCE JPL L[, h CJst Slhr(,r) Sc~lar Array Prole t (r~t mred by OTA June 19771
420 ● Solar Technology to Today’s Energy Needs

MODULE ASSEMBLY AND ENCAPSULATION

Finally, the process of connecting cells

together into arrays and encapsulating them

to protect the cells from the weather must

be reduced by a factor of 10 from current

costs to about $0.12/watt.

91 A variety of

techniques have been proposed and the cost

reduction seems feasible, but the exact

technique which will be used is not yet

clear.

Thin Films

The nonsilicon thin-film technologies

which show the greatest potential for

reaching the cost goals early in the 1980’s

are all based on the CdS/Cu2S heterojunction cell. Much more work has been done on

the problem of reducing the cost of manufacturing CdS/Cu2S than on any other thin

film.

Cadmium sulfide cells are produced commercially in the United States by Solar

Energy Systems (SES) of Newark, Del. These

cells are produced in batch processes92 a nd

hermetically sealed in glass. Their efficiency

is 3.2 percent with an array efficiency of 2.5

percent. 93 SES is attempting to keep their array prices competitive with the market price

of silicon arrays. An eariy prototype cell is

shown in figure X-12.

No technical barriers to scaling up the

current manufacturing procedures are foreseen, but a significant amount of “process

development” will be required to bring

prices below $1,000/kW.94 Researchers at

Westinghouse estimate that a factory based

on this process capable of manufacturing

cells for $1 to $2/watt could be producing

commercial products within 2 years of a

decision to initiate the project.95

“See table X-6

‘

2

F A Shlrland, Westinghouse Research Labs,

private communication, Mar. 26, 1976

‘3S DiZlo (President, SE S) private comr:]unication,

Apr 7 1976.

“Ibid .

95F. A Shirland, Westinghouse Research Labsr

private communlcatlon, Mar. 26, 1976.

Figure X.12.—Thin-Film Cadmium Sulfide-Copper

Sulfide Solar Cells

PHOTO: Courtesy of the University of Delaware

Photon Power, Inc., of El Paso, Tex., is

developing a chemical spray process which

forms cadmium sulfide solar cell panels directly on hot float-glass as it comes out of

the glass factory.

Photon Power has completed a pilot plant

in El Paso for testing the technique. If the

process works as well in large- scale production as it has in laboratory tests, the facility

will be expanded into a smalI manufacturing

plant which, it is hoped, will be able to produce arrays which can be sold for $2 to

$5/watt by 1980. 9

’ Low costs are possible

because all of the processes in cell manufacturing (cell growth, junction formation, ap9’G. Rodrick, (President, Photon Power, Inc.),

private communication, March 1978
Ch. X Energy Conversion With Photovoltaics ● 421

plying contacts, and encapsulation) involve

spraying a series of chemical layers onto hot

glass moving through the plant on a continuous conveyor. Laboratory devices produced with a similar process have yielded

5.6-percent efficiencies, and cells with 8- to

lo-percent efficiencies appear possible. ”

Even higher efficiencies may result if the

prom i sing resuIts of experiments mixing zinc

with cadmium can be integrated into the

process.

Photon Power is working with LibbyOwens-Ford (a part owner of the company)

to design a process which can be attached

to a float-glass plant. A preliminary calculation indicated that a plant costing about

$140 million would be able to produce 2

G We

/yea r for $0.05 to $0.15/watt.9 8

The major technical challenge in increasing

output will be finding a way to increase the

speed of the spray application process from

the 2 cm per minute in the pilot plant by

about an order of magnitude to match the

rate at which glass is produced from a flatglass facility.99 It will also be necessary to

“G A Samara (Sandia Laboratories, Albuquerque),

Proceedings, ERDA Semiannual Photovoltaic Advanced Ma reria /s Program Review A4eetlng, Wash I ngton,

D C , Mar 22-23, 1977

“j F jordan, Photon Power, Inc , International

Conference on Solar Electricity, Toulouse, France,

April 1976

“j F Jordan, Photon Power, Inc , private communlcatlon, April 1976

determine how much of the cadmium not

initially captured on the glass can be recycled (this is important since cadmium is expensive and toxic) and to determine how

well the hydrogen chloride, sulphur, and

sulfurous acids can be recycled.

The French National petroleum company,

Compagnie Francaise des Petroles, owns

controlling interest in Photon Power. LibbyOwens-Ford and D. H. Baldwin Co., own

minority interests.

Patcentre International of Hartfordshire,

England is working on a spray process very

similar to Photon Power’s. They report S. Spercent efficiency for their laboratory devices, and hope to market a commercial

product in 1980. ’00

A number of other cells, usually based on

heterojunctions between an element in

group III and group V of the periodic table,

are being investigated as candidate thin film

cells, but few are beyond the stage of basic

laboratory research. The present performance of some of these experimental devices

is shown in table X-2.

IOOG Kaplan, IEEE Spectrum, “Power/Energy Prog-

ress Report, ” IEEE Spectrum, Vol 15, No 1, january

1978, p 51

MATERIALS AVAILABILITY AND TOXICITY

Enthusiasm about cells based on mate

rials other than silicon must be tempered to

some extent by uncertainties abou‘t the

health hazards which they may present and

about the limits imposed on their production by U.S. and world supplies of component materials. Both cadmium and arsenic,

used in GaAs cells, are toxic and while it

may be possible to reduce the hazards they

present to manageable proportions and

whiIe both materials are already used extensively in commercial products and manufacturing, it clearly will be necessary to examine these hazards with some care before

recommending an energy system which

wouId significantly increase the use of these

materials near populated areas. Domestic

supplies of both cadmium and gallium will

be sufficient to supply annual production

rates in excess of several thousand

megawatts a year but production beyond

this level could tax domestic supplies and, in

the case of cadmium, known world reserves

limit the ultimate potential of CdS/Cu2S
422 ● Solar Technology to Today’s Energy Needs

devices to about the level of current U.S.

energy consumption.

SILICON

Silicon is nontoxic and in plentiful supply

(about one atom in five in the Earth’s crust is

a silicon atom), although current production

rates of purified silicon are not adequate to

support a large solar industry. The manufacture of silicon devices with present techniques involves the use of a number of

hazardous chemicals (PH3

, BCl3, H2S2, HCI,

HCN) .

101 Existing State and Federal laws

should be sufficient to ensure that releases

of these materials into the air and water are

kept to acceptable levels, although vigilance will be needed to ensure compliance

with these regulations. Meeting the standards may add to the cost of the devices.

CADMIUM

Cadmium is a cumulative heavy-metal

poison with a half-life in the human body of

10 to 25 years. Cadmium poisoning is believed to lead to accelerated aging, increased risk of cancer, heart disease, lung

damage, birth defects, and other probIems.

102 Chronic exposure to airborne cadmium can lead to emphysema and other respiratory problems. 103 Cadmium, however, is

used in many commercial and industrial

products; it is used for corrosion protection

on bolts and screws, in paints, plastics, rubber tires, motor oil, fungicides, and some

types of fertilizers.104 Increased use of cadmium resulting from large-scale manufacture of CdS/Cu2S cells could result in in10’] G. Holmes, et al , “Environmental and Safety

implications of Solar Technologies,” Proceedings,

1977 Annual Meeting American Section of the /nternationa/ Solar Energy Society, Orlando, Fla., june 1977,

p. 28-7

‘O’N A Esmen, et al., University of Delaware, Environmental Aspects of Cadmium Sulfide Usage in

Solar Energy Conversion– Part P– Toxicological and

Environmental Health Considerations – A 13ib/iography, NSF/RANN, SE/C I 34872 /T R73/5, june 1, 1973,

Section I I

‘OJHolmes, op. clt , p, 287.

‘

04 Esmen, op cit., section II & IV

creased release of cadmium from mining, refining, and manufacturing of the cell, and it

would increase the amount of cadmium

present in products located near populated

areas, thereby increasing the risk of exposure in the event of fires, accidents, or the

demolition of buildings.

More stringent standards may be needed

both in manufacturing processes involving

the material and in permitting usage of the

material in commercial products. At present, cadmium is not subject to any environmental controls, but under both the Toxic

Substance Control Act (P. L. 94-469) and the

Resource Conservation and Recovery Act

(P. L. 94-580), EPA has jurisdiction over its

regulation which, if instituted, could include

both solar and other household uses.

It is apparently possible to significantly

reduce the cadmium released in the manufacturing process, and it appears that with

proper encapsulation CdS cells can be used

in residential areas with minimal hazard. 1

0 5

Exposure to the material would only occur

during fires, accidental breakage, or building demolition. The acceptabiIity of such exposure can be judged better when meaningful standards have been developed.

U.S. production of cadmium in 1970

could support the annual manufacture of

cell arrays with a peak output of 5,000 to

20,000 MWe (assuming cells are lo-percent

efficient). World production is about five

times greater than U.S. production. 106 T h e

higher figure applies to the spray process for

manufacturing cells, which results in cells

about 6 microns thick. Significant increases

in cadmium production may be achievable,

however, if demand increases. Identified

U.S. reserves of cadmium are sufficient to

produce cells with an annual output equal

to the current U.S. consumption of electricity. Known world reserves are about five

times greater than U.S. reserves. ’07

‘

05 Esmen, op. cit

) ObH .j Hovel, IBM, Semiconductors an d

Semimeta/s, op. cit., p. 219.

107R A Heindl, Minera/ Facts and F’rob/ems, U.S.

Bureau of Mines, U S. G.P.O ,1970, p 515.
Ch. X Energy Conversion With Photovoltaics ● 423

GALLIUM ARSENIDE

Undisassociated GaAs is harmful but apparently not highly toxic. A lethal dose for

an average adult is about one-third kg (0.7

lb). ’08 To ingest this much GaAs, a person

would have to eat the amount of CaAs in

about 20m2 (200 square feet) of fIat-plate arrays or the amount of GaAs in a field of concentrating arrays covering about 3 acres,

clearly a Herculean task. The coatings and

protective encapsulation placed on cells

should be able to reduce any hazards associated with normal operation of GaAs devices to acceptable levels.

The major danger arises when the

material disassociates as a result of a fire or

some other accident, since many arsenic

compounds are highly toxic and recognized

carcinogens, 109 110 The AS20 3 which would

be released in a fire could contaminate land

and water near the fire site. Since the cells

wouId most probably be used in connection

with high concentrations of sunlight, care

must be taken to ensure that the materials

do not vaporize and escape if a breakdown

in the cell cooling system occurs. The

amounts of arsenic used in a concentrating

collector, however, wouId be extremely

1‘aBased on l-13j0 of 4,700 mg/kg body weight cited

In the Regtstry of Toxic Effects of Chemical Substances, 1975 Edltlon, U S Department of HEW,

N IOSH

‘“’N I Sax, Dangeroqs Properties of lndustrla/

Materials, Fourth Edition, Van Nostrand Reinhold Co ,

1975, pp 420-421

1‘“George L Waldbott, Hea/th Effects of Envlronmen?a/ Pollutants, C V. Mosby Co., 1973, pp.

202-203

PERFORMANCE OF CELLS

Since the output of cells varies as a function of temperature, it is necessary to compute cell temperatures in order to obtain an

accurate estimate of the output of cells installed in various types of collectors. The

temperature of the cells depends on the effective heat-transfer coefficient of the

system used to provide cooling. In simple

flat-plate systems, the heat loss from the

small. A device with a concentration ratio of

1,000 would, for example, use only about

0.16 gm per m2 of collector area. This concentration is 250 to 1,500 times smalIer than

the concentration of AS203 recommended

by the U.S. Department of Agriculture for

weed control. 111

Gallium supplies should not place a si g-

nificant constraint on the use of GaAs devices. U.S. consumption of gallium in 1973

was 8.5 metric tons per year, most of which

is imported. If this amount of GaAs were

used to produce 50-micron-thick cells used

in tracking collectors producing concentration ratios of 1,000, the arrays would have a

peak output of about 10 GWe at an efficiency of 20 percent. These arrays would have

an average output of about 1 percent of the

average output of all electric-generating

facilities in the U.S. in 1977. 113 Domesti c

production of gallium could be increased

substantially if an attempt is made to extract the gallium associated with coal,

aluminum, and zinc ores. A recent study indicated that the United States could produce about 600 metric tons/year of gallium

from these sources. ’ So the gallium resource is ample. World resources-of gal

are about 1.1 x 105 metric tons.}‘5

‘ 1‘USDA Herblclde Manual, 1965

‘“Y C M Yeh, j PL, private communication,

25, 1975

1

l‘H. j Hovel , IBM, Semiconductors

Semimeta/s, op. cit , ~ 219

lium

Apr.

and

‘“R N. Anderson,” Available Supply of Gallium and

Arsenic, NASA-Langley, Contract Order No L42953A,

1976

f‘‘H j Hovel, IBM Semiconductors and Semimeta/s,

Op Clt , p 220

IN REAL ENVIRONMENTS

front (and possibly also the back) of the arrays provides adequate cooling. In concentrating devices, it is usually necessary to provide more sophisticated cooling systems.

These systems can be passive [i. e., large,

finned radiating surfaces attached to the

cell), or active cooling can be provided by

pumping liquids across the back of the cell.
424 . Solar Technology to Today’s Energy Needs

PASSIVE COOLING

The heat-transfer capabilities of a variety

of passive heat exchangers have been

measured, although much more work must

be done to obtain adequate data in this

area. The results, shown in table X-8, are expressed in terms of an “effective heattransfer coefficient” ke where

ke=[rate of heat removal (kW/m2

of heat exchanger)]/(T – Ta) (x-3)

In this, ke varies with wind speed and thus

depends not only on the type of heat exchanger attached to the cells, but also on

the air circulation possible in each installation.

Table X-8.— Effective Convective Heat-Transfer

Coefficients [ke

] for a Variety of Cooling

Systems

Device Wind velocity ke

(kWjm’OC)

Air circulating passively through metal pan

in back of cells . . . . 0 0.015

Same as above . . . . . . . . ‘ ‘average’ 0.025

Flat plate with finned

metal heat-reject ion

surfaces . . . . . . . . ‘‘average’ 0.30

Active water cooling

with ‘ ‘simple flow’ . . — 1-3

Active water cooling

with “impingement

cooling’ . . . . . . . . . — 3-1o

SOURCE Table prepared by OTA from data supplied by F T

Bartels, (Spectrolab, Inc ,) Mar 1976.

In order to obtain a relation between cell

temperature T and insolation level I, an

energy balance is written

(x-4)

where a is the absorptivity of the encapsulated cell and Ta is the ambient air temperature. The value of I is given by the

following relations for f tat-plates or concentrating systems:

I

I

where:

I D = direct norma l

(kW/m

2

)

Ø i = angle between the

mal to the cell

solar intensity

Sun and the norEquations (X-2, X-3, and X-4) can be combined to yield an expression for cell efficiency in terms of insolation level:

ACTIVE COOLING

If water is pumped through a heat exchanger attached to the cells, the value of

Ke can be made as high as 3 to 10 kW/m2 “C.

With such high rates of heat removal, cell

temperatures can bz maintained at 150

0 F

(65 ‘C), even at concentration ratios near

1,000. The removed thermal energy available in the cooling fluid (QA

) is given by

where I is defined as before. UL is the heat

loss coefficient which differs with each collector design. This equation assumes the

entire receiver area is covered with cells. Tf

is the average temperature of the cooling

fluid (a more sophisticated equation considering cell coverage ratios less than unity

and the difference in inlet fluid temperature

is developed in chapter VIII.

The cell temperature (T) is given by

and the cell efficiency (n) is given by
Ch. X Energy Conversion With Photovoltaics . 425

PHOTOCHEMICAL ENERGY CONVERSION

Photochemical energy conversion has

many of the advantages of photovoltaic

energy conversion and, in addition, the advantage that the chemicals may be stored

for later use. However, the technology is not

as well developed as photovoltaics, and

much research remains to be done. The nascent state of photochemical energy conversion is compounded by the fact that public

awareness and Government funding are

both low, and thus research has been for the

most part confined to a few universities,

In 1972, Fujishima and Honda announced

the discovery of a process by which light

energy incident on an electrode suspended

in water could be used directly to convert

the water into hydrogen and oxygen without

any noticeable degradation of the electrode.

116 The original Japanese work has

generated a considerable amount of interest

and a number of other materials have been

examined. 117 118

A system being studied by research teams

of the Allied Chemical Corporation and

Massachusetts Institute of Technology is il-

‘“A Fu]ishlma andhK Honda, “Electrochemica l

Photolysls of Water at a Semiconductor Electrode,”

Nature 238, july 1972, pp 37-38

‘

 1‘K L Hardee and A J Bard, /, Electrochern Soc.,

~~q, 215 (1977)

1‘EM Wrlghton and J. M. Bolts, “Characterlzatlon

of Band Positions Photoelectrodes for the Photoelectrolysls of Water, ” paper delivered to the American

Chemical Society, San Francisco, Calif , September

1976, and /, Phys, Chem.,/X), 2641, 1976.

‘‘qHydrogen Production From Solar Energy, SITREP

Energy R&D, Report No. 154, Navy Energy and Natural

Resources R&D Off Ice, Feb 18,1977.

lustrated in figure X-13. In this system,

hydrogen is produced at the platinum

cathode and oxygen is generated at an

anode made from a semiconductor material

such as T1O3 or CaAs. Some work has also

been done on systems in which both electrodes are semiconductors. Other techniques for generating hydrogen have also

been demonstrated. Researchers at the

California Institute of Technology have

demonstrated that hydrogen is released

when light strikes a complex Rhondium

compound. 20 Research at the University of

North Carolina at Chapel Hill has Ied to the

development of a ruthenium compound

which can split water into hydrogen and oxygen when applied in a monolayer to a glass

surface and exposed to sunlight. ’z’ All of

these processes now exhibit very low efficiencies, and long-term stability has not

been demonstrated. Almost no work h a s

been done to determine the potential cost

of such systems.

The photosynthetic process used by

plants to convert sunlight into storable fuel

sources is clearly a photochemical system

with great potential. Work is underway to

better understand the basic chemistry of the

process and, of course, there is increasing interest in the use of plant materials as a fuel

source. The use of biological materials as an

energy source is beyond the scope of the

current study.

1]OM Simon, “UNC Professor Patents Solar Energy

Process,” C/rape/ Hill Week/y, june 1976.

‘“’’Gray Discovers Rhodium Compound a t

Caltech, ” The California Tech, Oct. 7, IW7, pp. 1,4.

28-.LI. I2 O - 28
426 ● Solar Technology to Today’s Energy Needs

Figure X-13. — Photochemical Energy Conversion

Phoioelectrolysls

H 2 0

PlatIn um Photocatalytic

electrode

*

Window

Light

f

SOURCE

Goodenough, J B (Professor, Oxford Unlverslty, England) “The Opt Ions for

Using the Sun,” Techrrology Flev/ew (Ml T.) 79(l), OctoberlNovember 1976,

pp 62.71
Chapter Xl

ENERGY STORAGE

Chapter Xl.—ENERGY STORAGE

Page Page

Major Design Choices . . . . . . . . . . . . . . . . . . . . . 429 Appedix Xl-A. . . . . . . . . . . . . . . . . . . . . . . . . . .487

Thermal Storage . . . . . . . . . . . . . . . . . . . . . . . . .432 Appendix Xl-B . . . . . . . . . . . . . . . . . . . . . . . . . . .488

Overview . . . . . . . ......................432

Low-Temperature Storage 0o

to 150°C(32o

to 302°F) . ........................43 2

Sensible-Heat Storage in Water. . .......432

Sensible-Heat in Rocks. . ..............441

Latent-Heat, Low-Temperature Storage ..442

Concentrated Solutions . ..............445

Thermal Storage at lntermediate and

High Temperatures . ................447

Refractory Bricks. . ...................447

Steel Ingot Storage . ..................449

Heat-Transfer Oii Thermal storage .. ....451

Refined Fuel Oii Thermal Storage . ......451

Latent-Heat Systems. . ................453

Environmental Concerns . .............458

Thermochemical Storage. . ..............459

Background . . . . . ....................459

Design Alternatives. . .................461

Summary . ..........................46 4

Electric Storage . . . . . . . . . . . . . . . . . . . . . . . . . .464

Mechanical Storage Devices . ............466

Battery Storage. . ......................469

Lead-Acid Batteries. . .................470

Advanced Batteries. . .................472

Power Conditioners. . . . . ................477

Design Alternatives. . .................477

System Performance. . ................480

Appendix Xl-C . . . . . . . . . . . . . . . . . . . . . . . .*..496

LIST OF TABLES

Table No. Page

I. Proposed Thermal Storage Materials .....433

2. Phase-Change TEC Materials in the LowTemperature Regime With Melting Points

Above 75°C (16 7

o

F) . ..................443

3. Candidate High-Temperature Thermal-Energy

Storage Materials Without Phase Change .449

4. Commercial Organic and inorganic HeatTransfer Agents.. . ....................452

5. Properties of Latent-Heat Thermal Storage

Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . .456

6. Candidate Chemicat-Energy Storage

Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . ..462

7. Conventional Hydroelectric Capacity

Constructed and Potentiai at Existing

Dams. . . . . . . . . . . . . . . . . .. .............469

8. Economic Specification (5-hr Battery) ....471

9. Load-Leveling Battries: Candidates and

Characteristics; Developers and Demonstration Dates . . . . . . . .....................473

10. Loss Mechanisms of iron-REDOX

Batteries . . . . . . . . . . . . . ................477

11. System Cost Estimates for Near-,

Battery System Costs. . .................481 Intermediate-, and Long-Term . . . . . . .. ...482
B-1. Thermal Properties of Soils . ...........492

C-1. Assumptions for Hot Fuel Oil Thermal

Storage, Single Family House . . . . . . . . . . 498

C-2. Assumptions for Therminol-55/Rock

Thermal Storage . . . . . . . . . . . . . . . . . . . . . 498

C-3. Assumptions for Steel-Ingot Thermai

Energy Storage . . . . . . . . . . . . . . . . . . . . . . 500

C-4. Containment Materials . . . . . . . . . . . . . . . . 501

C-5. Latent-Heat Storage Tank Assumptions. . 501

C-6. Assumptions for NaOH Latent-Heat

Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502

C-7. Assumptions for NAF/MgF2 Latent-Heat

Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502

LIST OF FIGURES

Figure No. Page

1. Possible Locations for Storage Equipment

in Onsite Solar Energy Systems. . ........430

2. Vertical Tank in a Drilled Hole With Foamedin-Place Insulation . . . . . . . . . . . . . . . . . . . .. 434

3. Installation of insulated, Underground, Storage

Tank at Solar Heated and Air-Conditioned

Burger King, Camden, N.J.. . . ...........435

4. installation of Fiberglass Underground

Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436

5. Cost of Buried Tanks . . . . . . . . . . . . . . . . . . . 437

6. Megatherm Pressurized-Water Heat-Storage

Tank . . . . . . . . . . . . . . . . . . . . . ...........439

7. Predicted Performance of an Aquifer Used

for Thermal Storage . . . . . . . . . . . .........440

8. Potential Sites for Aquifer Storage

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441

9. Osmotic Pressure Engine . . . . . . . . . . . . . . . 446

10. Heat of Mixing Engine . . . . . . . . . . . . . . . . . . 447

11. Low-Temperature Thermal Storage Cost

per kWht Versus Storage Capacity . ......448

12. A High-Temperature Thermal Storage

Device Designed for Residential Use ... ..450

13. Steel-ingot, Sensibie-Heat Storage System 450

14. Steei-ingot Temperature Profiles at Various

Times in a Typical Cycle. . ..............450

15. The High-Temperature Heat Storage System

at the Sandia Total Energy Experiment. . . . 454

16. Design of “Therm-Bank” Space Heater , .. 454

17. Philips Latent-Heat Storage System With

Vacuum Multifoil Insulation. . ...........455

18. Thermodynamic Behavior of Candidate

Latent-Heat Storage Salts ..... .........457

19. Use of a Sodium Heat Pipe With a LatentHeat High-Temperature Thermal Storage

System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458

20. Typical Thermochemical Storage

Technique . . . . . . . . . . . . . . . . . . . . . ......460

21. High-Temperature Thermal Storage Cost

per kWht Versus Storage Capacity . ......465

22. An isometric View of an Underground

Pumped Storage Plant . ................467

23. Conventional Hydroelectric Capacity Potential at Existing Dams. . .................468

24. iron-REDOX Battery Structure and Plumbing

Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

25. Model of iron-REDOX Battery Facility. .. ..478

26. The Elements of a Power Conditioning

System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

27. Efficiency of a Solid-State Inverter as a

Function of Load . . . . . . . . . . . . . . . . . . . . . . . . . 480

28. Power-Conditioning Cost Versus Power .. 483

A-1. Permissible Cost of Storage Equipment

as a Function of Energy Prices During

Storage Charge and Discharge . . . . . . . . . .487

B-1. Thermal Conductivity of Insulation. .. ...490

B-2. Annual Thermal Losses From Uninsulated

Storage Tank . . . . . . . . . . . . . . . . . . . . . . . . . 493

B-3. Rate of Heat-Loss to Ground . ..........493
Chapter Xl

Energy Storage

MAJOR DESIGN CHOICES

Energy can be stored in thermal form by heating or chilling liquids or

solids; in mechanical form by using mechanical or electrical energy to pump

water to high reservoirs, spin flywheels or compress air; and in chemical form

by driving battery reactions, producing hydrogen or other chemicals to generate heat, or by distilling solutions. This chapter discusses a range of storage

technologies which could have a major impact on the cost and performance

of onsite solar energy systems during the next 10 to 20 years; it does not attempt to review all possible storage technologies.

Most of these approaches require specialized storage equipment, but in

some cases it may be possible to integrate storage into mechanical structures which serve other functions. Careful architecture can increase the inherent ability of walls and floors, for example, to store thermal energy.

Energy can be stored at a variety of points in an onsite solar system and

some of the opportunities are presented in figure Xl-1. The options for the

heat engine system are most complex:

1. Energy can be stored at relatively high temperatures before it is used by

a heat engine. In this form, high-temperature storage is equivalent to a

2.

3.

It

supply of fossil fuel.

Heat rejected by the engines can be stored at relatively low temperatures.

Electricity generated by the system can be stored in batteries or other

electric storage devices.

is unlikely that all three types of storage would be used in a single instal I at ion.

Storage systems can provide a useful buffering role, regardless of whether solar

energy is used, since the timing of demands

and the timing of generation desirable for

peak performance of generating equipment

seldom coincide, Most of the equipment discussed in this chapter was developed for systems in which solar energy played little or

no part.

Some of the uses of storage are:

1. Storage in solar devices can be used to

provide energy during cloudy periods

and at night. Storage can also be used

to facilitate starting large solar turbine

systems in the morning by preheating

the equipment and to allow a gradual

cooling of the system when it is closed

at night. It can also mitigate the rapid ,

temperature changes which can result

from sudden fluctuations in the Sun’s

intensity during periods of partial

cloudiness.

2. Storage equipment can be used to

make more effective use of generating

equipment. As noted earlier, without

storage the output of generating equipment must be continuously adjusted to

meet fluctuating demands. This means

that generating equipment is either idle

or operating at part capacity much of

the time— resulting in higher electric

costs since capital charges must be

paid on the equipment, even if it is not

used. Operating plants frequently be

low full capacity also means that the

429
430 ● Solar Technology to Today’s Energy Needs

Figure Xl=1.—Possible Locations for Storage Equipment in Onsite Solar Energy Systems

Thermal

Collector

Thermal

Loads

Low

Temperature

Storage

I A

Thermal

Collector

Chemical Transport

High

Temperature

Storage

Heat

Engine

Photovoltaic

Cells

Cell

Cooling

I

Low

Temperature

Storage

Electric

Loads

Thermal

Loads

Hot Water Transport Electric

Electric

Storage

Temperature

Storage I

I

Transport

Electric

Loads

Thermal

Loads

Thermal Transport
Ch. Xl Energy Storage ● 431

generators are not operating at peak efficiency. Most large coal and nuclear

plants cannot readily be adjusted to

meet changing loads; demand fluctuations must be met with generating

equipment which burns oil or gas—

fuels which are becoming scarce and

expensive.

Generating capacity can be reduced with

storage equipment if the storage is filled

while capacity exceeds demand, and discharged during periods of high demand. In

electric utilities, this means that gas- and oilburning plants can be replaced by storage

charged from coal or nuclear plants functioning at close to their top output all year.

In the case of solar collectors, it means that

collectors can be sized to meet average

demands instead of peak demands.

With the exception of pumped hydroelectric storage, no electric storage* device is

now economically attractive to electric utilities. The rising cost of oil and gas as well as

progress in storage technology may reverse

this situation in the near future however,

and the industry will demonstrate a number

of advanced systems during the next few

years. The possibilities have been reviewed

in two recent studies sponsored by the Electric Power Research Institute (EPRI).l 2

Electricity which will eventually be used

for electric resistance heating can be stored

very inexpensively by using the electricity to

heat water or bricks in onsite storage devices. EIectric air-conditioning can also be

—

* The term “electric storage” IS used throughout this

chapter to mean storage which IS charged by and

which discharges elect rlclty, even though the energy

In the storage device IS not I n the form of electricity

‘Ralph Whitaker and j Im Blrk (E PRI), “Storage Batteries The Case and the Candidates, ” EPR/ /ourna/,

October 1976, p 13

‘An Assessment of Energy Storage Systems Suitable

for Use by E/ectr~c Utllltfes, EPRI project 225, ERDA E

(11 -1 }2501 , ) Uly 1975

“stored” inexpensively in tanks of ice or

chilled water.

Storage in this form will not be used unless prices to consumers are changed during

the day to reflect the fact that electricit y

costs less to generate during off peak hours

at night than it does during the day when

demands are large. These simple storage

devices are extensively used in Europe and

Great Britain, where such “time-of-day”

rates have been in use for many years and

are beginning to be marketed in the few

parts of the United States where these rates

are being introduced. 3

(The circumstances under which storage

devices can be used economically in loadIeveling applications are discussed in appendix Xl-B.)

3. Storage can improve the performance

of heating, cooling, and other energyconsuming equipment in much the

same way that it can reduce the cost of

generating electricity. Without storage,

the equipment must be large enough to

meet peak demands. This means that

the equipment must be operated at less

than its maximum capacity much of the

time, increasing the need for generating

equipment and decreasing system efficiency. Storage can have the additional

benefit of permitting heat-pump devices and air-conditioning devices to

operate when ambient conditions are

most favorable. Air-conditioning systems, for example, are much more efficient at night when ambient air temperatures are relatively low.

3Wi II iam H. Wilcox, statement delivered to the

Pennsylvania Public Utlllty Commlsslon (7 6

P, R.M. D -7), jUIY 25,1977
432 Solar Technology to Today’s Energy Needs

THERMAL STORAGE

OVERVIEW

There are three basic approaches to storing thermal energy:

●

●

●

Heating a liquid or solid which does not

melt or otherwise change state during

heating. (This is called “sensible-heat”

storage, and the amount of energy

stored is proportional to the system’s

temperature. )

Heating a material which melts, vaporizes, or undergoes some other change

of state at a constant temperature. (This

is calIed “latent-heat” storage. )

Using heat to produce a chemical reaction ‘which will then release this heat

when the reaction is reversed.

Equipment for storing energy as sensible

heat can be simple and relatively inexpensive if fluids are stored at temperatures below 400 o F. One difficulty with sensibleheat storage is that it can be difficult to ensure a constant output temperature.

If a constant temperature is desired to

operate a heat engine, or for some other purpose, two separate storage tanks are required: one to store the hot liquids and one

to store the low-temperature fIuids emerging

from the engine.

Latent-heat storage can supply energy at

constant temperature from a single container and can usualIy store greater amounts

of energy in a given volume or weight of

material. The materials used, however, are

relatively expensive and problems are encountered in transmitting thermal energy into and out of the storage medium.

Chemical storage techniques can be used

at a great variety of temperatures and have

the advantage of allowing storage of reduction products at ambient temperatures

(eliminating the need for expensive insulation). Chemical energy can also be transported conveniently. Recovering energy

from storage could be expensive, however,

if expensive catalysts are required. Chemical

storage can be expensive if some of the

chemicals which must be stored are in the

form of gases requiring large pressurized

tanks.

A number of promising reactions are being examined, however, and there is reason

to be optimistic that an attractive technology can be developed. Research in this area

is in a formative stage.

Table Xl-1 summarizes some of the materials and approaches which have been suggested for thermal energy storage,

LOW-TEMPERATURE STORAGE

0° to 150°C (32° to 302° F)

Sensible-Heat Storage in Water

A variety of techniques have been examined for storing relatively low-temperature

thermal energy, but the use of water as the

storage medium for liquid systems has been

the dominant approach and is likely to remain so for at least a decade. 4 5 Most solar

heating and hot water systems use an insulated hot water tank located in the building equipment room or buried in the ground.

Figure Xl-2 shows a cross section of a typical

instalIation, and figures Xl-3 and Xl-4 show

the installation of steel and fiberglass tank.

Tanks can be made from a variety of materials, and the costs of a number of commercially available containers are summarized

in figure Xl-5. It may be possible to reduce

the cost of large tanks significantly by simply lining an excavation with a watertight

‘C L Segaser (Oak Ridge National Laboratory),

Thermal Energy Storage Materials and Devices, OR NLHUD-M IUS-23, August 1975

‘George C. Szego, “Hot Water Storage Systems

Croup Report, ” i n Proceedings of the Workshop on

Solar Energy Storage Subsystems for the Heating and

Cooling of Buildings, NSF-RA-N-75-041, ASH RAE, Apr

16-18,1975, pp 17-23.
Ch. Xl Energy Storage 433

Table Xl-1 .—Proposed Thermal Storage Materials

— —..—

Temperature Regime

200o

-350 oC (392°-662oF)

0“-15 “C (32 0-500 f=) 30o

-150 oC (86°-302oF) (heat engines and

Storage (stores cooling (process heat and low- process heat, absorption 400 ”-1,000 oC(752o

-1,832oF)

type for air-conditioning) temperature heat engines) air-conditioning ) (heat engines)

— ..—— -. -— ————

Sensible — water

heat

Latent – C1 4

/ C1 6

heat paraffin

— 1 -Decanol

—other paraffIns

— Inorganic salt,

hydrate eutectics

— ice

Chemical

react ion

—pressurized water

— rocks

— Inorganic salt,

hydrate eutectics

(e. g., CaCI2 6 H20 )

—organic compounds

(e. g., paraffin &

CC14)

—metal hydrides

(e. g., LaNi5H2

)

—fuel oil

—organic heat-transfer

liquids (e. g.,

Therminol, etc. )

— rocks

—steel

—pressurized water

— NaOH

— rocks

—steel

—heat-transfer salts

(e. g., HITEC)

— in organic compounds

(LIH, NaOH, KN02

/

NaN 02

)

—eutectic salts

(LiF, NaF, etc. ]

CO + H2‘CH4 + H2 0

2 S 03 = 2S0 2 + 02

—.

(and possibly insulating) material. Plastic insulations (such as polyurethane) can simply

be floated on the surface of the thermal lake

thus produced.

Insulation can represent a significant part

of the cost of small water tanks, but in very

large devices (i. e., in systems capable of

holding more than about 30,000 k W ht o r

about 160,000 gal. ) the insulating value of

dry earth surrounding the tank may be adequate. The insulating value of dry soil 10

meters (33 feet) thick is roughly equivalent

to that of a layer of polyurethane foam 30

cm (12 inches) thick. Very dry, low-conductivity soil would be equivalent to 1.3 m (4.3

ft) of polyurethane. The heat conduction of

moist soil should decrease to this value as it

is heated by energy escaping from the tank

and dries out. b Since most buildings are

located in areas where ground water is quite

deep, earth insulation may be able to provide the bulk of the insulation required for

large thermal storage systems. It must be

recognized, however, that it can take as

‘j Shelton, “Underground Storage of Heat In Solar

Heating System s,” So/ar Energy, 17 (2), 1975, p 138

much as a year for the earth around a large

storage tank to reach equiIibrium by heating

and drying, and a considerable investment

of energy may be required to achieve this

equiIibrium. ’ Earth insuIation is examined in

greater detail in appendix Xl-B.

The value of a sensible-heat storage system is increased if it is able to return energy

at a temperature close to the temperature at

which fluids were delivered from the collectors.

One way of doing this is simply to use two

storage tanks, one of which holds water at a

relatively low temperature (i. e., at the temperature of fluids returned from heating

radiators) and another which holds fluids

emerging from the CoIIectors, This is more

expensive, although it does not necessaril y

require doubling the cost. In a large system,

several tanks may be needed to provide adequate storage. All that is needed in this circumstance is to maintain one empty tank

for shifting liquids from hot to cold storage.

‘Shelton, op clt , p 143
434 . Solar Technology to Today’s Energy Needs

Figure Xl-2. -Vertical Tank in a Drilled Hole With Foamed= in= Place

Insulation (for cohesive soils only)

Vent

Q

Welded nipples for

input-output, heat

exchangers, vents,

instruments, etc.

Steel tank shell

w/fiberglass coating

Alternate shells:

Fiberglass pipe

asbestos cement pipe

reinforced plastic

mortar

precast concrete pipe

\

~ 5’ – 15’ Diameter

Typical Capacities

4’ Diameter x 10’ Depth – 940 Gallons

6’ Diameter x 12’ Depth – 2,538 Gallons

8’ Diameter x 16’ Depth — 6,015 Gallons

10’ Diameter x 30’ Depth — 17,624 Gallons

Vertical tank in a drilled hole foamed-in-place

insulation (for cohesive soils only)

SOURCE: E. E. Pickering, “Residential Hot Water Solar Energy Storage,” Proceedings of the Workshop on Solar

Energy Storage Subsystems for the Heating and Cooling ot Buildings, NSF-RANN-75-041, Awl 1975, P P.

24-37

436 ● Solar Technology to Today’s Energy Needs

Figure Xl-4.— Installation of Fiberglass Underground Tanks

During Construction, a 1,500gallon underground water storage tank is eased into position

at a prepared excavation. The tank, made of lightweight resin-reinforced fiberglass, is one

of the two installed as part of the solar climate control system.

SOURCE: September 1976 Solar Engineering, page 23.

Such a device would require a control system and a series of adjustable valves.

In most single-tank systems, the cold

water returning from a heating system mixes

with the hot water in the storage tank, gradualIy lowering the temperature of the fluids.

It would be desirable to maintain a temperature gradient across the tank. A recent set of

measurements on the behavior of a typical

vertical cylindrical tank indicated that while

the water in the tank did not maintain a

perfect “stratified” temperature gradient,

the hot and cold liquids did not mix completely, and a substantial temperature gradient remained. ’

Most techniques suggested for increasing

the temperature gradients possible in single-

‘Warren F. Philips and Robert A. Pate, “Mass and

Energy Transfer in a Hot Liquid Energy Storage Systerns, ” Proceedings, 1977 Meeting of the American

Section of the International Solar Energy Society,

Orlando, Fla , june 6-10,1977, p. 17-6.

tank systems involve the use of internal partitions or one-way valves inside the tanks.9

Another method being studied involves

maintaining a gradient in the density of a

salt mixture inside the tank. Heated, high

concentrations of salt remain near the bottom of the storage tank if the drop in density

due to heating is offset by the higher density

resulting from the salt mixture. System stability has been difficult to maintain and experiments are continuing.

Given that the technology of large thermal-storage devices is simple, and its potential for energy savings so great, the small

amount of work done in the area is astonish-

‘Sui Lin, “An Experimental Investigation of the

Thermal Performance of a Two-Compartment Water

Storage Tank,” Proceedings, the 1977 Annual Meeting

of the American Section of the International Solar

Energy Society (l SE S), Orlando, Fla., june 6-10, 1977,

p. 17-1.

IOD. L. Elwell, “Stability Criteria for Solar (ThermalSaline) Ponds,” /SES, p. 16-29.
Ch. Xl Energy Storage ● 437

I

.

0

0m

b

.*

o

0

N

o

T

a)

m

‘al
438 . Solar Technology to Today’s Energy Needs

Ing. Possibly the field is not sufficiently

romantic.

It is possible to store water at temperatures above the boiling point if pressurized

tanks are used. A number of such pressurized storage systems are available in European markets’ and a device manufactured

by the Megatherm Corporation of East Providence, R. l., is now available on the U.S.

market. The Megatherm device, which is illustrated in figure Xl-6, stores water at temperatures up to 280° F (138 ‘C). 12 13 T h e

device is sold to institutions which can use

interruptible electric service or take advantage of “time-of-day” rates (see chapter V).

Water storage is probably not an attractive option for storage above 1500 to 200‘C

(300 0 to 400° F) since the pressure required

would greatly increase the cost and danger

of operating such systems. Local ordinances

frequently require all water tanks which

operate at temperatures above 2000 F, contain more than 120 gallons, or require more

than 2 X 1 0

5 Btu/hr inputs to comply with

ASME low-pressure heating boiler codes. ”

Pressure above 50 psia may require the presence of a trained operating engineer.

An EPRI study examined the feasibility of

using steam accumulators to store heat for

later use in a standard steam-electric generating plant and concluded that in this application, storage systems using fuel oil as

the storage medium were less expensive. 5

It may also be possible to store very large

amounts of low-temperature thermal energy

by pumping hot water into contained underground aquifers, as illustrated in figure Xl-7.

‘1A W Goldstern, Steam Storage /nsta//ations,

Pergamon Press, 1970.

‘*The Megatherm Corporation, East Providence,

R.1 , )Uly 1976

1‘Therma/ Energy Storage Materials and Devices,

OR NL-HUD-MIUS-23, August 1975, pp. 9-10.

14 ASME, “Heating Boilers, ” ASME Boi/er and Pres.

sure Vesse/ Code, Section IV, New York, N. Y., 1968.

1‘An Assessment of Energy Storage Systems Suitab/e

for Use by E/ectric Uti/ities, EM-264, E PRI Project 225,

ERDA E (11-1 }2501, Final Report prepared by Public

Service Electric and Gas Company, Newark, N j , Vol.

11, Jllly 1976, pp 4-45

If a deep aquifer is able to withstand high

pressures, it may be possible to store fluids

at temperatures as high as 200‘C (3920 F),

but it is more likely that somewhat lower

temperatures will be used. 16

It should be possible to recover 70 to 90

percent of the energy injected and to maintain a reasonable thermal gradient across

the aquifer (the warmest water will tend to

fIoat to the top of the structure).

Since the only investment required for

such a storage device is a series of wells for

injecting and withdrawing water, storage

costs can be very low. There is some disagreement about the cost of constructing

such systems, but costs could be as low as

$0.03/kWh t

17

-- with power costs in the range

of $5/kW.18 Pumping energy should be in the

range of $0.01/kWh (1970 dollars).

Aquifers adequate for thermal storage applications are found in wide areas of the

country (see figure Xl-8). It should be possible to use aquifers of brackish water as well

as freshwater wells and, since there is little

net consumption of water in the storage

process, the technique will not deplete the

water resources of a region or lower water

tables. The environmental impact of these

systems has, however, never been systematically addressed.

While a number of theoretical studies of

aquifer storage systems have been undertaken, 192021 there have been few field tests.

One large-scale experiment has been under-

“W. Hauz and C F Meyer, “Energy Conservation:

Is the Heat Storage Well the Key, ” Public Ut///eses

Fortnight/y, Apr. 24,1975.

“General Electric Corporation, Heat Storage We//s

Using Sa/ine and Other Aquifers, presentation to the

U.S. Department of the Interior, Mar 5, 1976

1

‘General E Iectric Corporation, op. clt

“C. F. Meyer and D K. Todd, “Conserving Energy

with Heat Storage Wells, ” Environmental Science and

Technology, 7, p512,

2 0C. F. Tsang, et al,, Numerica/ Mode/ing of Cyc/ing

Storage of Hot Water in Aquifers, EOS, 57,918

“C. F. Tsang, et al,, “Modeling Underground Storage in Aquifers ot Hot Water from Solar Power Systerns, ” Proceedings, the I SES 1977 Annual Meeting, p.

16-20.
Ch. Xl Energy Storage 439

—

I

x
440 . Solar Technology to Today’s Energy Needs

Figure Xl-7.— Predicted Performance of an Aquifer Used for Thermal Storage

200

160

120

80

40

0

Injection Temperature

i

I

A Daily cycle (24 hours)

O Semi-annual cycle, partial

penetration

v Semi-annual cycle, full

penetration

● Yearly cycle, full

penetration

1 2 3 4 5

Cycle

40

0

.

.

A Daily cycle (24 hours)

O Semi-annual cycle, partial

penetration

.

v Semi-annual cycle, full

penetration

. Yearly cycle, full

.

penetration

1 1 I 1 1

1 2 3 4 5

Cycle

Temperature at the end of each production period (min!mum pro- Percentage of energy recovered over energy Inlected versu>

ductlon temperature) versus cycle number cycle number

SOURCE’ C, F Tsang, et al., “Modeling Underground Storage in Aquifers of Hot Water from Solar Power Systems, ”

ISES Proceed{rrgs of the 1977 Annual Meeting, page 16-20.

DRAWfNG FROM: Walter Hauz and Charles F Meyer, “Energy Conservation: Is the Heat Storage Well the Key?,”

Publlc UfWt~es Fortrr/ght/y, Apr 24, 1975, p 34.
Ch. Xl Energy Storage ● 441

Figure Xl-8. - Potential Sites for Aquifer Storage Systems

(Aquifers In the Shaded Areas Should Have Adequate Water Flow)

SOURCE: Geraghty, et al., Water At/es of the United Stares, Water Information Center, Port Washington, N. Y., 3rd Ed., 1973.

taken near Bucks, Ala. Approximately 2.4

million gallons of warm water were injected

into an aquifer and stored at a temperature

of 105” to 1070 F (41 0 to 42 “C) and stored

for 30 days. About 65 percent of the energy

was recovered when the water was pumped

out of the formation. 2 2 unfortunately, the

water used in the test was taken from a local

river and contained small clay particles

which began to clog the aquifer after about

2 million gallons (7.6 million liters) of water

had been injected. The test was stopped

when injection pressures became excessive.

The experiment will be repeated using

water from an aquifer in the same region

which does not contain clay particles capable of plugging the aquifer. If all goes well,

about 20 million gallons will be injected

over a period of 2 months.

Swedish engineers have recently suggested that it may also be possible to store

22 F MOIZ Department of C ivi I Engineering, Au bum

University, private communication, November 1977

large volumes of heated water in plastic

bubbles suspended in a lake.

Sensible-Heat in Rocks

Energy can be stored at low and intermediate temperatures by heating rocks held

in insulated containers. Rock storage is typically used with solar heating systems using

air to transfer heat from collectors to storage since the rocks can be heated by simply

blowing air through the spaces between the

rocks. (If Iiquid is used in the collectors, a

more elaborate heat-exchange mechanism is

required. ) Rock storage can be both simple

and inexpensive, but designing an optimum

system can be difficult since the performance is affected by the shape, size, density,

specific heat, and other properties of the

rocks used. 23

“W D Eshleman, et, al., A Numerical Simulation of

Heat Transfer in Rock Beds, ISES, Proceeding of the

1977 Annual Meeting, p. 17-21.

‘2 R.842 () - 2~
442 ● Solar Technology to Today’s Energy Needs

It may also be possible to store large

quantities of sensible thermal energy in underground rock formations using a technique which is essentially the solid-state

equivalent of the aquifer storage discussed

previously. A number of schemes have been

proposed for storing energy in this way:24 25

●

●

●

●

Digging deep parallel trenches into dry

earth (or land which is “dewatered”

with a pumping well) and filling these

trenches with crushed rock. The

crushed rock would be heated from a

series of distribution pipes buried with

the crushed rock, and heat would be

removed by blowing air through similar

buried pipes.

Excavating a large area in sandy soil,

depositing a layer of material which

can prevent ground water from entering

the excavation, and filling part of the

excavation with crushed rock. An insulating layer would be placed on top

of the rock. (This scheme would lead to

a significant change in local topography. ) Hot air distribution pipes would

be buried in the layer of crushed rock.

Digging tunnels through layers of sandstone or other porous rock in naturally

occurring formations. I n one proposal,

the rock is heated by sending hot air

through pipes located in an intermediate plane in the rock formation. The

air passes through the rock formation

and is returned through a piping network on planes above and below the injection plane. Heat is removed in the

same way when cold air is introduced in

the intermediate plane.

Caverns of crushed rock could be produced by drilling and blasting underground rock layers if the rock layers

available were not suitably porous. Pre-

“M P Hardy, et al , ‘ Large Scale Thermal Storage

In Rock Construct Ion, Utilization and Economics, ”

12th /ECEC Conference, p 583.

‘5M Rlaz, et al,, “High Temperature Energy Storage

In Native Rocks, ” Proceedings, the I SES joint Conference Sharing the Sun–Solar Technology in the

Seventies, Volume 8, p 123 (1976) Pergamon Press

Iiminary calculations have indicated

that performance of the storage bed

would be optimum if the rock particles

are about 0.3 cm (0.1 inch) in diameter.

It has been estimated that energy could

be stored in these formations at temperatures up to 500‘C (9320 F). The cost of the

system will vary from site to site, but it may

be possible to build devices for $0.03 to

$0.09/kWh and $150 to $400/kW, if the storage cycle involves removing air at a temperature of 500‘C above the temperature at

which it was injected.

2s If a temperature

swing of only 50‘C is used, storage costs

would be on the order of $.30 to $.90/kWh.

Latent” Heat, Low=Temperature Storage

An enormous variety of phase-change materials have been examined for possible use

in low-temperature storage systems . 27 28 29 30

The properties of a selected set of these materials are summarized in table Xl-2. Phase

change materials used in low-temperature

applications are of three basic types: inorganic salt compounds, complex organic

chemicals (such as paraffins), and solutions

of salts and acids. Water itself can be used

as a latent-heat storage medium to store

“coolness;” the latent heat of melting ice is

0.093 kWh/kg.

A successful latent-heat system must have

the following properties: 31

“Hardy, op. cit , p. 590.

“Maria Telkes, Thermal Energy Storage, IECEC 1975

Record, p. 111

28D. V Hale, et al , Phase Change Materials Handbook, NASA-CR-61 36. Lockheed Missiles and Space

Company, September 1971

“C L Segaser, MIUS Technology Evaluation: Thermal Energy Storage Materia/s and Devices (ORN LHUD-M IUS-23), August 1975, p. 28

‘OH C. Fisher, Thermal Storage Applications of the

IceMaker Heat Pump, Oak Ridge National Laboratory,

9-30-76. (Paper prepared for presentation at Pennsylvania E Iectric Association, Harrisburg, Pa. )

“Harold Lorsch, Conservation and Better Utilization of Electric Power by Means of Thermal Storage

and Solar Heating – Final Summary Report ,

NSF/RAN N/SE/G 127976/PR73/5, j uly 31, 1975 Some

phrases taken verbatim.
Ch. Xl Energy Storage ● 443

Table X1-2.—Phase-Change TEC Materials in the Low-Temperature

Regime With Melting Points Above 75°C [167°F]

TEC material

— — —

Mg(N 03)2 6 H20 .

Ba(OH )2. 8H20. .

N H4Br(33.4% )

CO(NH2)2 . . . . .

Acetamide

( C H3CON H2 ) .

Naphthalene

( C1 0H 8 ) ., ... . .

Propionamide

( C2H 5CON H2 )

—

Latent heat of

Melting point phase change

Class Lab test* “C “F (Cal/G) (Btu/lb)

———. .

inorganic compound S 89 192.2 NA NA

inorganic compound G 82 179.6 63.5 114.3

inorganic eutectic G 76 168.8 NA NA

organic compound s 82 179.6 NA NA

organic compound G 83 181.4 35.3 63.5

organic compound G 84 183.2 40.2 72.3

— —— —

NOTES NA — not available

‘S — satisfactory performance

G — good performance

SOURCE Hoffman (Oak Ridge National Laboratories), prepared for OTA, 1976.

A melting point within the desired temperature range.

A high heat of fusion (this reduces storage volume and material demands).

Dependability of phase change (a melt

should solidify predictably at the freezing point and shouId not supercool).

Small volume change during phase

transition (a volume change makes

heat-exchange difficult, and can place

stress on the storage containers; most

materials increase in density when they

freeze, but water and gallium alloys expand).

Low-vapor pressure (some materials

have high-vapor pressures near their

melting points, placing stress on containers).

If the latent-heat medium is a mixture,

it must remain homogeneous; i.e., its

parts should not settle out.

has proven difficult to combine all of

these properties in a single system.

The rate at which energy can be withdrawn from many phase-change storage systems is limited by the fact that the storage

medium usualIy begins to solidify on the surface of heat exchangers; the layer of solid

material acts as an insulator. Designs for increasing effective heat exchange areas have

usually involved “microencapsulation” (in

which the storage medium is separated into

a number of smalI containers suspended in a

heat exchange medium) or shallow trays.

The General Electric Company has recently proposed another approach. In their system, the phase-change materials is contained in a series of long, cylindrical containers which rotate (typically at 3 rpm) to

keep the material mixed and to maintain a

uniform temperature throughout the mixture. GE claims that with this approach,

solidification begins at a number of nuclei

distributed throughout the Iiquid and not on

the walls of the cylinders,

INORGANIC SALT COMPOUNDS

Inexpensive salt mixtures have the potential of requiring up to 100 times less volume

for low-temperature storage than a simple

sensible-heat, water-storage system. The disadvantage of all such systems compared
444 . Solar Technology to Today’s Energy Needs

with simple water storage is the need to use

more complex heat exchangers, nucleating

devices, and corrosion-resistant containers

(if corrosive salts are used). The two categories of salt solutions which have received

the most attention are inorganic salt

hydrates and clathrate and semiclathrate

hydrates.

If the concentrations of the components

of a mixture are adjusted so that the mixture

attains its lowest possible melting point, the

mixture is termed “eutectic. ” In such a mixture, melting occurs at a constant temperature. 32

Inorganic salt hydrates are crystalline

compounds of the general form S • nH2O ,

where S is an anhydrous salt. The hydrate

dissolves when these compounds ar e

heated, absorbing energy.

Clathrate and semiclathrate hydrates are

compounds in which water molecules surround molecules of materials which do not

strongly interact with water. These materials

melt in the range of 00 to 30‘C (30 to 860 F)

and have heats of fusion which are in the

range of 78-118 Btu/lb; most have not been

studied in detail. 33 Materials suitable for use

in connection with space heating (melting

points in the range of 30° to 48‘C (86° to

1180 F) and heats of fusion in the range of 66

to 120 Btu/lb.) include Na2S 04 . 10H20

(Glauber’s salts), Na2H P 04 . 12H20, and

CaC l2 ● 6 H20. Materials suitable for storing

“coolness” (melting points in the range of

130 to 18‘C (550 to 750 F) and heats of fusion in the range of 70 to 80 Btu/lb. ) include

eutectic salt mixtures such as mixtures of

N a2S 04

/10H20/NaCl, and N a2S O4/10 H2O/-

KCI.34

“See, for example, Walter J. Moore, Physica/ Chemistry, 3rd edition, Prentice-Hal 1, 1964, p. 148.

“M. Altman, et a[,, Conservation and Better Utilization of Electric Power by Means of Thermal Energy

Storage and Solar Heating, Final Summary Report,

NSF/RANN/SEGl 27976/PR73/5, University of Pennsylvania, National Center for Energy Management

and Power, July 31, 1973, pp. 6-51

“Segaser, op. cit., p, 30.

‘ST. E. Johnson, MIT, private communication, May

1978, R. Stepler, “Solar Lab Soaks Up Sunshine With

Exotic New Materials,” Popu/ar Science, June 1978,

pp. 96-98.

Many of the clathrates examined do not

appear to melt in temperature regions useful

for heating or cooling applications.

A technique for encapsulating a proprietary mixture of Glaubers salts, fumed silica,

and other chemicals (melting temperature

730 F (230 C) in a polymer concrete shell has

been developed by the Massachusetts institute of Technology working in cooperation

with The Architectural Research Corporation of Livonia, Mich., and the Cabot Corporation of Billerica, Mass. The storag e

elements are formed into units the size of

standard ceiling tiles (2 ft x 2 ft x 1 in) and

are designed to be installed as ceiling tiles in

passively heated solar buildings. They store

about 0.7 kWh/ m

2 of ceiling area, and

should sell wholesale for about $32/m2 in initial production (about 13 times the cost of

standard acoustical ceiling tiles). The devices thus have an effective storage cost of

$39/kWh storage capacity. MIT does not expect prices to fall rapidly; apparently material costs already represent a large fraction

of the cost of production. While the tiles

can be hung on hangers similar to those now

used for acoustical ceiling tiles, their greater

weight, which is 54kg./m2

, requires the use of

heavier gauge hangers.

The tiles, which will be marketed under

the trade name “Sol-Ar-Tile,” have been

demonstrated in a 900 ft2 passively heated

solar house built by MIT’s Architecture Department. Timothy E. Johnson, who heads

the project, reported in May 1978 that tiles

suffered no deterioration after accelerated

lifetime testing, in which the tiles underwent

2,400 freeze-thaw cycles. The building uses

specially designed window blinds which refleet sunlight from the southern windows to

the ceiling. Johnson claims that the phase

change medium is nontoxic. 35

ORGANIC COMPOUNDS

Organic compounds can also be used for

storing energy as latent heat. These materials have the advantage of relatively high

heats of fusion, and few of the materials examined present problems of supercooling or

high vapor pressures. Unfortunately, some
Ch. Xi Energy Storage 445

of the most attractive organic materials

under consideration (e. g., paraffins) have a

relatively large volume change upon melting (nearly 10 percent in some cases), are

flammable, and can cause stress cracking if

the containment vessel is not constructed

from a material as strong as steel. Experimental paraffin storage systems, however,

have been operated successfully. 36

Materials suitable for heating include artificial spermaceti (manufactured by Lipo

Chemicals) and paraffin wax (possibly mixed

with carbon tetrachloride). These materials

melt in the range of 350 to 50‘C (95 0 t o

1220 F), and have heats of fusion on the

order of 40 to 90 Btu/lb.37 Materials such as

Acetamide (CH 3CONH 2

), Naphthalene

( CIOH8

) and Propionamide (C2H,COHN2) can

be used to store energy at slightly higher

temperatures, melting in the range of 820 to

83‘C (180 0 to 1830 F) and having heats of fusion in the range of 55 to 72 Btu/lb. 38 Materials suitable for storing coolness include

paraffins and olefins with freezing points in

the range of 30 to 80 C and heats of fusion in

the range of 65 to 85 Btu/lb. 39

Concentrated Solutions

Concentrated solutions can also be used

to store low-temperature energy without a

phase change. It has been suggested, for example, that solutions of LiBr utilized in absorption air-conditioner systems could be

used to store solar energy in the “generator”

portion of an absorption unit. 41 42 42 It has

“A D Fong and C W Miller, “Efficiency of Paraf -

f~n Wax as a Thermal Energy Storage System, ” Proceedings, the 1977 Annual Meeting of I SE S, p 16-6,

“lbld , p 33

“C A Lane, et al , Solar Energy Subsystems Emp/oyIrIg Isothermal Heat Storage Materials, ERDA- 117, UC94a May 1975

‘

9 Segaser, op clt , p 33

‘“j Baughn and A jackman, Solar Energy Storag e

W(thin the Absorption Cyc/e. Paper delivered to the

ASME meeting in New York, November 1974

4

‘M Semmers, et al , L/quid Refrigerant Storage in

Absorption Air-Conclitioning. Paper delivered to

ASME meeting In New York, November 1974

“E H Perry, “The Theoretical Performance of the

Lithium-Brom ide-Water Intermittent Absorption

Refrlgeratlon Cycle, ” Solar Energy 17 (5), November

1975, p 321

also been proposed that a device similar in

operation to an absorption air-conditioner

could be used to provide heat from such

storage, using an “absorption heat pump.” 43

All such systems would require three storage

tanks: one for the concentrated solution,

one for water, and one for the dilute solution. The storage would not require insulation.

It is believed that approximately 65 Btu/-

pound of LiBr) could be stored in a system

which uses sunlight to distill a solution of 66

percent LiBr to 54 percent.44 A major drawback of using LiBr is the high cost of the material, but further study may reveal other

less expensive salts with acceptable properties.

SALT STORAGE FOR OSMOTIC PRESSURE ENGINES

Energy can be generated from the os -

motic pressure developed between salt solutions and freshwater. A system based on this

principle is illustrated in figure Xl-9. The

concentrated saline solutions produced for

use in such equipment can be stored in uninsulated tanks which can be quite inexpensive. A cubic meter of a salt solution comparable to water from the Dead Sea (27 percent salt by weight) can produce 1 to 21⁄2

kWh in a reverse osmosis engine. ” Figure

Xl-5 indicates that large tanks can be purchased for less than $20/m3

, and therefore

brine storage can be achieved for about $ 8

to $20/kWh (or more if storage must also be

provided for the freshwater distilled from

solution). The use of covered ponds could

result in substantially lower storage costs.

SALT SOLUTIONS FOR ENGINES

USING LATENT HEAT OF MIXING

Engines can be operated from the latent

heat released when concentrated solutions

‘

] Letter from Dr. Gary Vllet (University of Texas,

Austin) to Dr Albert R Landgrebe (ERDA), jan. 5,

1975

44Cary Vliet, ibid,

4 5S Loeb, et al,, “Production of Energy from Concentrated Brines by Pressure Reduced Osmosis: I I Experimental Results and Projected Energy Costs, ” journa/ of Membrane Science, (1), p. 264(1 976)
446 “ Solar Technology to Today’s Energy Needs

Figure X1-9.—Osmotic Pressure Engine

High Pressure Pump

SOUROE: OTA.

of some types of salt are mixed with water

(see figure XI-10). Energy is released when

water is introduced and aqueous solutions

are formed. ’b A study of this effect has

estimated that if energy is stored in the form

of dry NaOH, the density of the energy

stored is 135 kWh/m3

, and if energy is stored

in the form of dry ZnCi2

, CaCl2, MgCl2, LiBr,

and LiCl, the energy storage density is about

80 kWh/m3

.

CHEMICAL REACTIONS

There is growing interest in the possibility

of storing energy for low-temperature applications in chemical form, but work is in a

very preliminary stage and no practical

systems have yet emerged. ” 46 A recent ex-

“N. isshiki, et al., “Energy Conversion and Storage

by CDE (Concentration Difference Energy) Engine and

System, ” Proceedings, the 12th Intersociety Energy

Conversion Engineering Conference, Washington,

DC., Aug. 28-Sept. 2, 1977 (American Nuclear Society,

La Grange Park, ill.), page 1117.

“G S. Hammond, “High Energy Materials by

Charge Transfer and Other Photochemical Reactions, ” ACS 122r7d Meeting, San Francisco, Cal if., September 1976.

48S. C. Talbert, et al., “Photochemical Solar Heating

and Cool ing,” Cherntech, February 1976, p. 122.

ploratory survey indicated that photochemical reactions can be competitive with other

low-temperature thermal storage systems if

they are capable of 25-percent conversion

efficiency and energy storage at more than

158 Btu/Ib. (88 cal/g), or 40-percent efficiency and 81 Btu/lb. (45 cal/g).

One of the few low-temperature reactions

which has been studied involves the use of

metal hydrides. The reactions are of the

general form M + (x/2)H2 ~ MHX

, where M

is a metal or alloy such as LaNi5

, SmCo5, or

FeTi. These materials are capable of storing

between 45 and 92 Btu per pound of hydride

(0.029 to 0.059 kWht/kg), if storage temperature is heId at 2000 F and initial hydride

temperature is 700 o

F.49

Energy is stored when the hydride is

heated, releasing the gas, and recovered

when hydrogen recombines with the metal.

Recent investigations at the Argonne Na4’G. G. Libowitz, “Metal Hydrides for Thermal

Energy Storage, ” Proceedings, the 9th Intersociety

Energy Conversion Engineering Conference, San Francisco, Cal if., Aug. 26-30, 1975, p. 324 (Quoted in

Segaser, pp. 37-38.)
Ch Xl Energy Storage 447

Figure Xl-10.— Heat of Mixing Engine

To Process

Loads 1

1

~

i-lot Water Storage

Condenser

Mixing Heat

r

Chamber Engine

To

SOURCE OTA.

tional Laboratory have demonstrated the

feasibility of hydride storage for both

heating and cooling applications ‘0

The possible costs of several of the lowtemperature thermal storage systems discussed in the previous sections are summarized in figure Xl-11. The techniques used to

compute these costs are explained in appendix XI-B,

THERMAL STORAGE AT INTERMEDIATE

AND HIGH TEMPERATURES

Table Xl-3 lists the properties of some of

the materials which can be used to store

thermal energy at high temperatures. Rock

storage was treated in the previous section.

The following discussion examines sensible

heat storage in refractory bricks, iron ingots,

and hot oils.

‘“James H Swisher, Director of the Dlvlslon of

Energy Storage Sy5tems, Of flee of Conservation,

ERDA, letter to OTA dated Mar 30, 1977

Refractory Bricks

Devices capable of storing energy in magnesium oxide bricks at temperatures up to

600 oC (1 ,1120 F) have been commercially

available in England and Western Europe

for many years; the original patents dat e

back to 1928. They are in buildings so that

customers can charge the storage from the

relatively inexpensive electricity available

in these areas at night; during the day ,

homes and offices can be heated from the

systems in the same way that a baseboard

resistance heater would be used. In 1973,

both Great Britain and West Germany had

installed enough such devices to provide

nearly 150,000 MWh of storage capacitys1 52

for leveling the loads placed on their electric utilities. Devices such as the one shown

in figure Xl-12 are beginning to appear on

the U.S. market in areas where time-of-day

5 IGunter Mohr, Electric Storage Heaters, AE CTelefunken Progress, (1970), 1, p 30-39

52) G Ashbury and A. Kouvalls, E/ectric Storag e

Heat/rrg: The Experience in Eng/and and Wales and ~n

the Federa/ Repub/lc of Germany, ANL,’E S-50(1976)
448 Solar Technology to Today’s Energy Needs

Figure Xl-11 .— Low-Temperature Thermal Storage Cost per kWht

Versus Storage Capacity

200

100

50

20

.20

.10

0.05

100

Single Tank Storage

—“- MultlpleTank Storage . ‘

‘, ,t

1000 104

Storage capacity (kWht)

10’

NOTE:

The storage untts would lose only about 5 percent of the energy

stored In the Interval Indicated. This cost IS based on precast

concrete and coated steel, and excludes 25 percent O&P
Ch. Xl Energy Storage ● 449

Table Xl-3.—Candidate High-Temperature Thermal-Energy Storage Materials

Without Phase Change

Sensible-heat storage between 77° F and 900° F

Density Price (1971 $) output

Material (lb/ft 3

) Btu/lb Btu/f t

3

($/100 lb) (Btu/$)

Al . . . . . . . . . . 168 200 34,000 29.00 690

A 12

( S 04) 3 . . . 169 202 34,000 3.11 6,500

Al 203 , . . . . . . 250 200 50,000 2.20 9,100

CaCl 2 . . . . . . . 135 135 18,000 2.20 6,000

MgO . . . . . . . . 223 208 46,000 2.80 7,400

KCI . . . . . . . . . 124 140 17,400 1.65 8,500

K2SO 4 . . . . . . 167 180 30,000 1.10 16,400

Na 2CO 3 . . . . . 160 265 42,500 4.00 6,600

NaCl . . . . . . . . 136 180 24,500 1.33 13,500

Na 2SO 4 . . . . . 168 247 41,500 1.50 16,400

Cast Iron . . . . 484 102 49,500 10.00 1,000

Rocks . . . . . . . 140 160 22,500 1.00 16,000

SOURCE M Allrnan, et al @rrSe~at~Ofl a~~ ~~~er u~lllza~lo~ of ~~ectrlc power ~Y Means Of ~~er~al .Emrgy Storage and

so/ar ~eatln~, Phase I .Su~~arY ~eport, NSF G127976, Unlverslty of Pennsylvania National Center for Enerqy

Management~nd Power, Oct 1, 1971, pp. 2-10

rates have been introduced. The units

typicalIy sell for $20 to $40/kWh. 53

Some thought has been given to using

these bricks to provide high-temperature

storage for a solar-powered gas turbine system. I n one proposal, helium from a receiving tower would be passed through a pressure vessel containing refractory bricks,

heating the bricks to about 530oC (986 0 F). It

is estimated that such a device could be

constructed for $11 to $14/kWht. 54

Steel Ingot Storage

A system for using steel or cast-iron ingots

to store high-temperature energy for use in a

steam electric-generating plant has been

proposed by Jet Propulsion Laboratory

(JPL). 55 56 This device, illustrated in figure

Xl-1 3, consists of an assembly of pipes with

rectangular external cross sections. Super5’) G Ashbury, et al., “Commercial Feasibility of

Thermal Storage in Buildings for Utility Load LevelI ng, ” presented to the American Power Conference,

Apr 18-20,1977, Chicago, Ill.

“W D Beverly, et al , “1 ntegration of High Temperature Thermal Energy Storage into a Solar Thermal

Brayton Cycle Power Plant, ” 12 IECEC Conference, p

1195

‘

% Beverly, op clt , p 1199

heated steam is passed through the pipes for

charging and discharging. It should also be

possible to maintain a significant temperature gradient along the length of the storage

unit for several days (see appendix Xl-B). The

predicted performance of a large device is

illustrated in figure XI-14. Like the MgO

(magnesium-oxide) storage system, this device has the advantage of great simplicity, it

has virtually nothing to wear out, no heat exchangers to clog, and no scarce or toxic materials are required. It has an advantage over

the brick storage system in that a pressure

vessel is not required to contain the heattransfer fluid —the steel pipes provide the

needed containment. For this reason, the

cost should be slightly less expensive p e r

unit of energy stored. 57

It should be possible to build a steel ingot

storage system with relatively Iittle develop56program Review, cC3fT)pari3tivt2 Assessment of ~rbita/ and Terrestrial/ Central Power Systems, OCtober

1975- January 1976, jPL, p 16

“R H Turner, j PL, “Thermal Energy Storage Using

Large Hollow Steel Ingots, ” Sharing the Sun: Solar

Technology in the Seventies, joint Conference,

American Section, International Solar Energy Society

and Solar Energy Society of Canada, I nc , Winnipeg,

Canada, Aug. 15-20, 1976, Vol 8, pp. 155-162.
450 Solar Technology to Today’s Energy Needs

Figure XI-12.—A High-Temperature Thermal

Storage Device Designed for Residential Use

A storage/heating unit installed in a home

high density mineral wool

thermal Insulation heat storage core

finish

cabin

metal

warm alr o

# of magnesite bricks

heating

elements (made

of 80% Nickel/

20°& Chromium

mounted on

ceramic supports)

Figure Xl-13.— Steel-Ingot, Sensible-Heat

Storage System

Return to solar collector

during charging; return from

load during discharge

I

- Distribution piping

Input from solar collector

during charging; input to

load during discharge

,. . . .

/ I

(nole diameters not to scale)

u t

quiet, low energy, squirrel cage fan

(actuated by room thermostat)

An interior view of the unit showing the

magnesium bricks, heating elements and air

blower

SOURCE Control Electric Corporation Burlington, VT

ment work since most of the properties of

the system can be computed with considerable precision. Since the system uses high-

-pressure steam, considerable care must be

taken if it is used in onsite applications, but

existing boiler codes should be able to ensure adequate safety. Lower pressures can

be employed if the system uses a heattransfer fIuid other than steam.

Figure Xl-1 4.—Steel-Ingot Temperature Profiles at

Various Times in a Typical Cycle

950°F Fully charged system temperature \

\ \

I

\

\

\

Ingot system length

(Steam path is many ingots long)

SOURCE:

R. H. Turner (JPL), “Thermal Energy Storage Using Large Hollow

Steel Ingots,” Sharing the Sun: Solar Technoloav in the

Seventies.

“.

Joint Conference, American SectIon, International Solar Energy

Society and Solar Energy Society of Canada, Inc. Winnipeg,

Canada, Aug. 15-20, 1976, Volume 8, page 160.
Ch. Xl Energy Storage 451

It may be possible to reduce the cost of

the system by replacing some of the volume

of metal with concrete. Concrete costs

about a third as much as steel and could

easily be formed around a matrix of separate steel pipes. The practical difficulties of

constructing such a system have not been

evaluated, however, The performance of the

system could be degraded significantly if

the concrete separated from the steel tubes;

this may create problems even though concrete and steel have nearly the same coefficients of expansion. Another difficulty

would be the relatively poor heat transfer

between concrete and steel. Concrete itself

has low conductivity, and cracks could further reduce its conductivity.

Heat-Transfer Oil Thermal Storage

Some of the sensible-heat storage systems

utiIize a mixture of rocks and a heat-transfer

fluid such as Therminol. The properties of

some common commercial heat-transfer liqu ids are Iisted in table Xl-4. Sandia Laboratories in Albuquerque chose a system using

Therminol-66 and rocks for storing energy in

its total energy system. This system, shown

in figure Xl-1 5, has been operated successfully since early 1976. A mixture of Caloria

HT43 and granite rock storage was chosen

by McDonnell-Douglas for storing energy

generated by their central receiver design.

Martin-Marietta chose to use a sensible-heat

storage system with two stages — a high-temperature stage for superheating, using

HITEC as the storage medium, and a lowtemperature stage using a heat-transfer oil.

Each stage has two tanks for high performance.

All heat-transfer oils share a common set

of problems. They all degrade with time,

and their degradation is increased rapidly if

they are operated above their recommended

temperature Iimits for any length of time.

This degradation requires a filtering system

and means that the relatively expensive oils

must be continualIy replaced. The oils also

can present safety problems, since they can

be ignited by open flames at temperatures in

the range of 3000 F (fire point) and have a

high enough vapor pressure to sustain combustion at temperatures in the range of 600 c

to 1,0000 F (ignition temperature), This

means that great care must be taken to ensure that the material is not overheated,

Dikes will be needed to prevent the material

from spreading if a leak should occur. Some

systems require an inert gas (such as nitrogen) over the liquids in the tanks to inhibit

reactions which might degrade the storage

material. The behavior of the rock-oil mixtures over long periods of time remains an

open question, since little experimental

evidence is avaiIable. The rocks may tend to

crack, and the apertures between them may

clog with degraded oil.

Refined Fuel Oil Thermal Storage

A thermal storage system proposed by

EXXON eliminates the problems of degradation and clogging by using a relatively inexpensive fuel oil without rocks.58 This system

uses specially refined oil that does not degrade with time, but it can only be used at

up to 530° F (277 ‘C). The oil is estimated to

cost $146/m 3 (installed, excluding operations

and maintenance) and, if necessary, can be

used as fuel at any time.59 Its specific heat is

0.795 kWh~Jm3

“C.bo

An EPRI study estimates the installed cost

of insulated tankage, including an inert gas

system to exclude oxygen, to be $91/m3 o f

oil for a two-tank system. Oil handling facilities, such as pumps, piping, and heat exchangers, are power related, rather than

energy related, and cost $288 per installed

k wth of capacity .61

“An Assessment of Energy Storage System5

Suitable for Use by Electric Utii[tles, EM-264, EPRI

Project 225. ERDA E (11-1} 2501, Final Report

Prepared by Public Service E Iectrlc and Gas Company, Newark, NJ

“lbld , pp 4-40

‘“ibid , pp 3-48

“ Ibid , pp 4-41 Converted from $144 kWe using O 4

kWe kWth and 1 25 O&P factor
452 ● Solar Technology to Today’s Energy Needs

Table Xl-4.—Commercial Organic and Inorganic Heat-Transfer Agents

Refined fuel

Therminol- Therminol- Caloria-HT- Dowtherm- Humble- oil

b

5 5

a

6 6

5

4 3

5 A

5

therm 5005 HITEC5

(see text)

Dow E. 1.

Producer Monsant o

c Monsant oc

EXXONC Chemical d Humble Oil Dupont EXXON C

Highest usable temp

(“C) = Tmax . . . . . .

Lowest usable temp:

(°F) . . . . . . . . . . .

(“c). . . . . . . . . . .

(°F) . . . . . . . . . . .

Fire point (°C) . . . . . .

Autoignition temp(° C)

Specific heat (Btu/lb

o

F)3 (or cal/gm°C) . .

Viscosity (lb/ft-hr)e 

.

Thermal conductivity

(Btu/hr-ft° F e 

. . . . .

Density (lb/ft3

)

e 

. . . .

Heat capacity (Btu/

ft3° F)e . . . . . . . . . . .

Cost ($/lb) . . . . . . . . .

cost ($/ft3 ). . . . . . . . .

Mills/Btu (assuming

AT = Tm a x

- 5 0

0Can d

perfect thermal gradient). . . . . . . . . . . . .

Mills/Btu (assuming

complete mixing and

allowing T max to fall

to (Tmax /2) + 25” C)

316

601

-18

210

354

0.72

1.1

0.065

43

31

0.38

16.34

1.1

2.2

343

649

-4

193

374

0.655

0.649

0.0612

50

32.8

0.81

40.50

2.3

4.6

316

601—

—

404

—

—

—

0.26

S.2f

6.4

260

500

-11

135

621

0.537

0.65

0.0645

53

28.5

0.71

37.63

3.5

7.0

a @mPlfed by Hoffman (ORNL) and Tas Bramlette (Sand la, Llvermore)

b

Energy in 011,” IEEE Power Englneenng Soc(ety Summer Meeting, Portland, Oreg., July 1976

c Requires nonoxldlzlng cover gas

d Requires pressurization for temperatures above 260”C

e Propefly at maximum usable temperature.

f AT = Tmax – 83°C

g AT = Tmax – 150”C

h AT max falls to (Tmax/2) + 75°C

316

601

-21

246—

0.7165

1.01

0.0655

41.3

29.6

500

932

142

288

—

—

0.4

112

44.8

0.25

28.00g

277

531—

—

—

0.70

—

0.68

—

38.21

4.13

0.99 0.26

2,0h

0.53
Ch. Xl Energy Storage 453

At least one design for such a hot-oil

energy storage system for use with a 1,000

M We nuclear powerplant has already been

completed, and the EPRI study classifies this

technique as “a near-term solution with certain economic advantages over other storage systems.”62

Latent-Heat Systems

Heat-of-fusion systems using inorganic

salt mixtures have a distinct advantage for

storing energy at high temperatures, since

they can reduce storage volumes and provide more energy at constant temperatures.

The major disadvantages have been the

costs of the materials required and the problem of developing adequate heat transfer

between the storage material and the working flu id. Two designs which have been used

in devices designed to store energy for space

conditioning are illustrated in figures Xl-16

and Xl-17, The Comstock and Wescott design uses relatively inexpensive materials:

NaOH mixed with corrosion inhibitors. The

unit shown consists of six moduIes containing sodium hydroxide which was heated

with electricity. The unit has been redesigned to use steel pipes rather than the

panels shown. 63 64 65 A similar approach has

been proposed by JPL for use in a central

station powerplant. I n their approach, a

bundle of tubes is imbedded in a long cylindrical tank (in the central station design, the

tanks were 60 feet long and 12 feet in

diameter) filled with sodium hydroxide. The

steam or other heat-transfer Iiquid is sent

through the tubes to extract or to supply

energy to the storage medium. The tubes

‘Zlbld , pp 3-51 The completed study IS referenced

as R P Cahn and E W N Icholson, Storage of OffPeak Therma/ Energy In 0;/, Approved by I E E E Power

General Committee, Paper No A76 326-9 Summer

1976

“Comstock and Wescott, Inc., “First Step of Heat

Storage Research Actlv[ty of Heat Storage Systems, ”

EE/ L3u//, June 1959

“Comstock and Wescott, Inc , “Promlslng Hea t

Storage Material Found Through Research, ” E.E/ Bu//.,

February 1962, p 49

“R H Turner (J PL), private communication, June 9,

1976

must be closely spaced to permit acceptable

rates of heat transfer since sodium hydroxide has a relatively small heat conductivity.

JPL estimated that such a system could store

52 MWht if the temperature swing were between 6500 and 4000 F and would cost

about $13/kWht.Gs A major problem with

these systems is that the highly corrosive

nature of NaOH (lye) demands expensive

containment to prevent leaks.

The Philips Corporation has investigated a

number of materials for possible use in a

phase-change storage system. Lithium fluoride has received the most attention because of its extremely large latent heat of fusion, but other less expensive materials have

also been examined for use in the Philips

design. ” Other fluoride compounds, for example, have extremely large latent heats.

The properties of a variety of salt compounds which might be considered for use in

phase-change storage systems are illustrated

in table X I-5 and their thermodynamic behavior is illustrated graphically in figure

Xl-1 8. It can be seen that the sodium hydroxide material appears to have an advantage

in the temperature regime appropriate to

conventional Rankine cycle systems, while

fluoride compounds (such as the NaF/MgF2

mixture) appear to have an advantage when

used in connection with engines operating

at very high temperatures such as Brayton or

Stirling cycle devices.

In general, the nitrates and nitrites are

relatively inexpensive and do not corrode

their containment vessels, but they tend to

decompose at temperatures above 4000 to

500 “C. The hydroxide eutectics can operate

at high temperatures, but become corrosive

and thus require corrosion-resistant alloys.

Carbonates have good thermophysical properties, but also decompose at high temperatures unless a cover gas of CO2 is used in the

tanks. Chlorides and fluorides have high specific heats, conductivities, and latent heats,

“R H Turner (J PL), private communlcatlon, June 9,

1976

“j Schroder (N.V Philips Aachen Lab ), Therrna/

Energy Storage, N V Phlllps publication
454 ● Solar Technology to Today’s Energy Needs

Figure Xl-15.— The High-Temperature Heat Storage System at the Sandia Total Energy Experiment

— Aphotograph by John Furber

Figure Xl-16.– Design of “Therm-Bank” Space Heater

Heater terminale

\

Inner tank cover

90URCE R E Rk., rrwn.l Smmp APPIIc@On W EnwvY ConsewMIII Comwoch md Wssc.11, Inc AD.(. 1975 Rwrlntad m

timbl~. *I 4, SAN07$iMb2 P8C942
Ch. Xl Energy Storage ● 455

SOURCE N V Phlllps
456 Solar Technology to Today’s Energy Needs

Table XI.5.—Properties of Latent-Heat Thermal Storage Materials

Storage material NaF/MgF 2 LiF/NaF/MgF 2

(mole %) NaOH (75/25) B2O3 46/ 44/ 10 NaN03 Lif

Melting point ‘C. . . . . . . 320a 832b

‘F. ., . 608 1530

Density at m.p. (kg/m3) . 1784 2190b

(most bulky phase)* . . . . (Iiq) (Iiq)

Heat of fusion ( A HPC). 0.0442c 0.174b

(kWh/kg) ., . . . . . . . . . 0.0442**

Specific heat at m. p. 5.89 x 10-4a 4.1 x 1O-4*••

sol id (Cp

) (kWh / kgoC) (below 295° C) ——

(above 295” C)

Specific heat at m .p.,

liquid (Cp

) (kWh /kg° C) 5.75 x 10-4C 4.07 x 10-4e

Heat capacity (m. p,-50° C

to m,p. + 50” C) (kWh/

m

3

).....................* 262 471

0.55f 1,10-0.55g

983 2400-1200

Material cost ($/ kWh capacity) (m. p. -50” C to

m.p. + 50° C) ., ., 3.75 5.10-2.55

450c 632d

842 1170

1571 c 2105d

(Iiq) (Iiq)

0.092d 0.226

(e)

4.48 X 1 0

-4d 4.88 X 10-4

(e)

5.09 X 1 0

-4d 4.88X 10-

4*••

205 578

0.20 2.20

312 4641

1.52 8,02

31Oc

590

1916c

(Iiq)

0.0481

(c)

5.06 X 10-4

● ☛☛

5.058 X 10-4

(c)

189

0.57

1098

5.81

845c

1553

1829c

(Iiq)

0.290

(c)

6.69 X 10-4

(d)

6.94 X 10-4

(c)

655

5.56h

10,161

1551

. Volume of storage conta[ner must be large enough to accommodate most bu Iky phase

. . Solld/solld phase change at 295° C (563° F)

. . . Estimate based on speclf[c heat of other phase

aKubaschewskl, O , et al (National Physical Laboratory, Mlddlesex), Metallurgical Thermochemistry Fourth E d Pergamon Press

Ltd , 1967

bschroder, J (N V Phlllps Aachen Lab) , “Thermal Energy Storage Using Fluorldes of Alkall and Alkallne Earth Metal s,’ Proceed/rigs

of fhe Symposium on Energy Storage The Electrochemical Soctety, Inc , 1976

cJanz, G J (Rensselaer Polytechn IC Institute), Mo/(en Sa/ts Handbook Academic Press I nc , 1967

dw{cks, c E and F E Block (U S Bureau of Mines), Therrnodynarn(c Properties of 65 E/ernents — The/r Ox/ales, Ha//ales, Carb/ijes

and Nlfrldes BuI Iettn 605, Bureau of Mines, 19(j3

eschroder, J ( N v Phlllps Aachen Lab), private communication, Jan 13, 1977.

fchem(cal Mar~e(l~g Reporter VOI 210, No 10, Sept 6, 1976 100 lb drums of U S PharmacoPla NaOH In truckload quantities

9$0 !jsl kg IS a cost estlnlate made by N V Pfllllps, based on (he use of waste rnaterlals from fertilizer rnartufacturlng present cost IS $1 1 (J / kg

hLltfllum Corporation of America quotatton, SerX 15, 1976, for 99 5 ° 0 LIF in lots greater than 5 tons This material IS proposed for use

In Phil Ips space heat storage system

m p — melt ng point

(Ilq)— hqu[d phase

but tend to be higher in cost and can have

corrosive properties. Phosphates and sulfates are very corrosive.

If the latent-heat storage system can be

located very close to the collectors, it may

be possible to use a heat-pipe system to convey the energy from a collector to storage.

Extensive surfaces would have to be affixed

to the heat pipes to produce sufficient heattransfer surface area in the storage medium.

This may be feasible since the latent-heat

systems are capable of storing a large

amount of energy per unit weight. The storage could be mounted directly on a tracking

dish, or it could be physically close to an

engine mounted at the top of a tower.

Heat pipes operate most effectively if

their working fluids have pressures in the

range of 1 to 10 atmospheres. Both sodium

and potassium have these pressures in temperature ranges of 6000 to 1,000 “C. The

technology of sodium-vapor heat pipes has
Ch. Xl Energy Storage 457

0

0

.05

.10

.15

.20

.25

.30

.35

.40

.45

.50

.55

.60

0

Figure Xl-18.—Thermodynamic Behavior of

Candidate Latent-Heat Storage Salts

Temperature of storage (°C)

100 200 300 400 500 600 700 800 900

of heat engines

Organic rankine engines I

100 200 300 400

SOURCE Table Xl 7

been thoroughly investigated, and pipes

made of relatively low-cost “type-304” stainless steel are predicted to have lifetimes of

10,000 hours. ” ‘9 This lifetime corresponds

to only a little more than a year of continuous operation for a generating system, and

further improvements are needed if an ac-

‘8G A A Asselman, et al , “Heat Pipes, ” Philips

Tech. Review, Vol 33, No 4 (1970), p 104

“C A A Asselman, et al , “Hea~ Pipes, ” PhI/ips

Tech l?e~ Iew, Vol 33, No 5 (1970), p 168

I Gas turbines

J \

500 600 700 800 900 ‘c

ceptable generating system is to be designed. Such improvements are expected,

but design research and much more operating experience is needed.

A Philips design employing a heat-pipe

and a phase-change storage system is illustrated in figure Xl-19. When the storage is

being “charged,” the liquid sodium flows to

the collector where it is vaporized and returns as a gas to the storage vessels. (EIectric

pumps for moving sodium without moving
458 Solar Technology to Today’s Energy Needs

Figure Xl-19.— Use of a Sodium Heat Pipe

With a Latent-Heat High-Temperature Thermal

Storage System

operator, and they do not appear to present

any serious safety problems. Release of the.

sodium from the system could be hazardous, but only very small amounts of sodium

are required in the system per-unit-of-power

output.

Unfortunately, there remains a substantial amount of disagreement about the performance capabilities of phase-change sysHeat from solar collectors

SOURCE: Drawn by OTA using N. V. Philips concept,

parts have been developed by the breeder

reactor program. ) The vapor condenses on

the storage containers, giving the energy of

vaporization gained at the collector and the

cycle begins again. When the system is being discharged, the vapor is generated by the

storage vessels and condensed in a heat exchanger sending energy to a heat engine. If

auxiliary power is needed to supplement the

solar energy, a separate heat exchanger can

be built into the heat-pipe loop to permit

running the engine from fossiI fuels.

If these low-pressure sodium or potassium

heat-pipe systems could be developed, they

would be very attractive. They should not

require extensive maintenance or a trained

exchangers, average cycle efficiency corrosion resistance, and development of lowcost materials have been resolved .’” On the

other hand, others are still having substantial development problems and feel that a

considerable amount of fundamental development work is needed. Only more research

and the fabrication and testing of real

devices will resolve these debates.

Environmental Concerns

The environmental problems associated

with the use of high-temperature thermal

storage devices have not been explored in

detail, although a preliminary survey of the

issues has been conducted. 71

Some of the oils proposed for use as heat

transfer fluids or as storage materials can be

explosive. Care will have to be exercised in

the construction and operation of these systems, particularly if they are integrated into

systems close to populated areas. Most oil

storage tanks must be covered with an inert

gas such as nitrogen to minimize the risk of

explosion when the oil is heated. Leaking

tanks could result in fires; earthen dikes or

dams would be required around large tanks

built above the ground. The risk would be reduced if underground storage were used.

Care would also be essential when the ther70). Schroder (N V Phlilps Aachen Lab ), private

communication, jan 13, 1977

“john G. Holmes, “Environmental and Safety implications of Solar Technologies” Proceedings, the

1977 annual meeting of the American Section of the

International Solar Energy Society, p, 28-5
Ch. Xl Energy Storage ● 459

ma storage materials are discarded after a

system is dismantled or when fluids are replaced if they have been damaged or degraded with repeated thermal cycles. The

oils would typically be dumped into city

sewage systems.

THERMOCHEMICAL STORAGE

Background

Recent interest in thermochemical reactions for storing energy has been motivated

primarily by a desire to find a way to store

and transport energy generated by nuclear

plants .

72 73 Like the heat of fusion storage

systems, chemical storage has the advantage of being able to produce heat at constant temperature. It has the additional advantage of not requiring insulated storage

tanks. Some chemical systems could allow

storage densities many times higher than

any other types of thermal storage. A variety

of reactions have been examined, and there

appears to be no technical barriers to using

a number of them in connection with solar

colIectors.

The problems remaining involve both the

need to understand much more about the

fundamental chemistry of some simple reactions which have never been examined i n

detail, and the engineering details of converting laboratory reactions into reliable

commercial products It is also possible to

use the energy stored in chemical reactions

to transport energy from colIectors to a storage vessel The “Solchem” process, for example, being examined by the Naval Research Laboratory, uses the SO3

/ S O2 reac7ZR schu Iten, et al , The Concept of N’uclear Hvdrogen Production and Progress of Woolf in the Nuc/ear

Research Center )uellch, paper presented at the 1 St

World Hydrogen Conference, Mlaml Beach, Fla , Mar

1-3, 1976

‘

) Jon B Pangborn, “ }iydrogen Energy TechnologyUpdate 1976,” In Energy Technology I I I proceedings

of the third energ y technology conference,

Washington, D C , 1976, p 1972

tion to transfer heat to a latent-heat storage

system. 74

Developing procedures which will be

useful for onsite applications may be difficult, since many of the reactions being examined are quite complex. Frequently, the

reaction in the collector is simpler to control

than the reverse reaction, In this case, a

series of distributed onsite collectors could

be used to feed a common collection pipe

network which operates an electric-generating device at a central facility, I f hydrogen

or other easily reacted materials are produced, the storage products could be used

easily in onsite facilities without trained

operators.

The basic chemical cycle employed is

shown in figure XI-20. A chemical (labeled

“A” in the diagram) is preheated in a counterflow heat exchanger and sent into the collector where it is separated into products

(“B” and “C” in the diagram) through a

chemical reaction. The heated-reaction

products are cooled to ambient temperatures in the heat exchanger. If the reaction

requires a catalyst in the solar collector, it

may be possible to store the products at ambient temperatures. If no catalyst is needed,

it may be necessary to store each reaction

product separately. The stored products can

then be piped to other sites where energy is

needed, When energy is to be extracted

from the system, the reaction simply proceeds backward at a lower temperature (Ie

Chateler’s principle). In the diagram, “B”

and “C” recombine to form “A “ If the orig

-

inal chemical (“A”) is valuable, it must then

be piped back to the collector. In som e

cases, the reaction must proceed throug h

In a recent paper, W. E. Wentworth and E

Chen presented an elegant approach for

evaluating and comparing thermochemical

“T A Chubb , “A Chemical Approach to Solar

Energy, ” to be publlshed In Cherntech, 6, p 654, (October 1976)
460 ● Solar Technology to Today’s Energy Needs

Figure Xl-20.—Typical Thermochemical

Storage Technique.

Collector

Energy I

from sun

Storage

L

A

Distribution

b # \ 4

Collection reaction User-site reaction

reactions. Their work provides the basis for

the analysis which follows. 75

The basic measures of merit for a thermochemical reaction are: 76

“w. E. Wentworth and E. Chen, “Simple Thermal

Decomposition Reactions for Storage of Solar Thermal Energy, ” Solar Energy 18(3), 1976, p. 205.

“I bid,, p. 208,

1

to

J

The reaction should be nearly complete

within the temperature range of available collectors. (In practical terms, it

would be desirable to have 95 percent

completeness at temperatures below

1,000 oC.)

2. The reverse reaction should be nearly

complete at the temperature at which

useful energy is to be extracted. (If the

reaction is to be used in connection
Ch. X/ Energy Storage 461

3

4.

5.

6.

7,

8

9

wit h

- a conventional powerplant, this

temperature would be approximately

500 “C; if a Stirling cycle or Brayton cycle device were to be used, the temperature should be closer to 800 “C.).

The reversible reaction should be able

to release energy for the user at temperatures close to those supplied by the

collector. (The collector temperature

should be as low as possible to minimize material problems and to maximize collection efficiency— in the following discussion, it will be seen that

this requirement will be met by reactions which involve large changes in

entropy. )

The energy absorbed per-unit-volume

of the products stored should be as

large as possible to minimize the volume of storage. It would be most desirable to be able to store the reaction

products in liquid form. This would

both reduce storage costs and the

energy losses in pumping the stored

material.

The reaction should be completely reversible and no side reactions should

occur to produce contaminants in a

closed-cycle system. These side reactions would tend to create products

which would accumulate and eventually poison the system.

Reactions should be fast.

None of the reactions involved should

require extensive development of new

chemical techniques. They should not

require expensive or elaborate equipment. This is of paramount importance

for onsite equipment not operated by

trained personnel.

The reaction products should not react

strongly with water or oxygen, since it

would be difficult to seal the system

against these materials.

The materials used should be inexpensive and should not require chemicals

for which shortages are likely to develop.

Design Alternatives

Most of the thermochemical reactions

which are now being examined for use in

connection with high-temperature storage

systems require fairly sophisticated reaction

apparatus which must be maintained by

trained personnel. As a result, these thermochemical systems will be limited to relatively large onsite systems, such as shopping

centers, industries, and communities. Research may develop reactions which do not

require such attention and the equipment

needed for existing systems may be simplified, but much more development work is

needed before assessment of this issue can

be made.

METHANE–STEAM

A variety of reactions have been proposed

for use in larger systems, and some of them

are summarized in table Xl-6. The reaction

which has probably received the most recent attention is the methane/syn-gas reaction. The methane reaction probably re -

quires the least development since the technology required for each step of the storage

process is commercially available and the

chemistry is well understood.

The Ralph M. Parsons Company, for example, has operated a device for converting

hydrogen and carbon monoxide to methane

for 3 years, producing nearly a million ft3

/-

day of methane. The equipment was designed as a part of a synthetic fuel plant,

where the first step would be partial combustion of coal to produce the “syn-gas”

combination of H2 and CO, and the second

phase would use the Parsons’ “methanation” process. 77

One potential difficulty of the methane/

steam process for onsite application is the

difficulty of controlling the reaction. The

thermal output from the reaction which gencrates heat can be throttled down to about

50-percent peak capacity without major dif-

“Charles Luttman (Ralph M Parsons Co.), private

communication, Aug. 6, 1976.
462 ● Solar Technology to Today’s Energy Needs

Table X1-6.—Candidate Chemical-Energy Storage Reactions

———

Reaction

Energy stored Cost of

Temperature per unit mass storof reaction Temperature of (VOI. ) of stor- age

in colIector ● user react ion ● age material mateo C o

F

n

T o C “F rial Comments

Btu/lb kcal/liter $/kWh

—

780 1,440 0.94 610 1,130 2,792 50

589

590

435

335

390

1,150 60

1,090 532 110

850 512

635 446 740

740 567 470

0.16

1.1

0.62

0.07

Products of the storage

reaction are gases and thus

V Olume IS large. Gas must

be stored under pressure.

Reactions are well known.

Nickel catalyst required. CO

+ 3H2 CH 4 + H2 0 IS a

methanation reaction.

Products stored as gas

Cost includes system cost

S 02 stored as liquid, 02 as

gas,

. See text for explanation of terms In the anal ysls of “temperature effl[ IPIIy Tc = 100‘ F has been used

SOURCES W E Wentworth and E Chen, “Simple Thermal Decomposlt [on React Ions for Storage of Solar Thermal Energy, Sular Energy

18(3), 1976

T T Bramlette (Sandla Laboratories, Llvermore), Survey of High- Temperature Thermal Energy Storage SAN D75-8063,

March 1976, pp 83-94

R S Hockett and R W Serth, “High Temperature Thermal Energy Storage System, ” 721h IECEC Conference, (1977), pp 510

ficulty, but control beyond the So-percent

reduction becomes difficult. Another major

problem is the relatively low-energy density

of the gas which must be stored. The H2 +

CO mixture holds approximately 60 Btu/ft 3

at atmospheric pressure, and methane holds

approximately 240 Btu/ft

3

. The price of

tanks for storing the coal and gas mixture

wiII dominate the cost of this type of storage. If large amounts of gas are to be stored

and underground caverns or abandoned gas

fields are available, underground storage is

clearly the most inexpensive approach. A recent JPL study estimated that hydrogen

could be stored in depleted gas fields and

aquifers for about $1/1 ,000 SCF,* in dis-

‘The abbreviation “SCF” stands for standard cubic

feet If the gas IS stored under pressure, the volume

wou Id be less th~n the “SCF”

solved salt caverns constructed for this purpose for about $3/1 ,000 SCF, and in mined

caverns for about $5.6/1 ,000 SCF .

78 T h e

energy storage costs would thus range from

about $17/106 Btu ($0.057/kWh t) of storage

capacity for gas field storage to about

$93/106 Btu ($0.32/kWhtO for mined caverns.

These underground storage systems

would not be available in many sites, They

could probably be used only in connection

with a very large plant, and then only if appropriate geology could be located. With

current technology, it would be necessary to

store the gas in pressurized tanks, In the

future, it may be possible to store hydrogen

78 Toshlo Fujlta (j PL), Underground Energy Storage

for E/ectric Uti/i(les Ernp/eying Hydrogen Energy Systems, June 1976, p VIII
Ch. Xl Energy Storage ● 463

in solid hydrides .79 A recent EPRI study indicated that hydrogen could be stored at 8 8

atmospheres for about $0.50/SC F

80 ( o r

$28/kWh t

) in the syn-fuel storage system.

Major development problems which must

be overcome for the methane/steam cycle

include the design of high-temperature receivers using nickel-base catalysts. The receivers must be capable of operating for extended periods with minimal maintenance.

Another unresolved issue is the question of

the extent to which the system will be stable

when the load or solar influx changes suddenly. There may also be difficulties with

side reactions which wouId lead to the accumulation of reaction products that would

poison the system. The seriousness of these

difficulties and the cost of overcoming them

cannot be determined without operational

testing.

MULTISTAGE PROCESSES FOR

GENERATING HYDROGEN

A number of multistage processes have

been suggested for generating hydrogen, but

most are cumbersome for onsite applications and involve several different reactions,

some of which require the addition of Iowtemperature “process heat” in addition to

the high-temperature processes. 8’ Two advantages of these muItistage processes over

single-stage hydrogen production are that

lower temperatures can be used and that the

two gases are released separately at different stages.

General Atomic Company, which in 1973

developed a computer program to find the

best combination of chemical reactions that

could form closed hydrogen-producing cy -

“G Strlck land and J J Reilly, Operating Manua/

for the PSE&G Hydrogen Reser\oir Containin g

Tita rJIum Hycfrlcfe, Brook haven National [Lab ,

February 1974

a’JUtJ/)zar)on ot C~ff-Peak Power to Produce /ndustr/a/ Hydrogen, EPRI 320-1, Final Report, prepared

by I nstltute of (;a~ Technology, August 1975

“M M E lsen~tadt and K E Cox, “ Hydrogen Production From SoJ~r [ nergy, ” So/ar [nergy, 1 7(1 ), 1975,

p 59

cles, reported to ERDA

the following cycle the

last fall that it found

most promising:

(1)

(2)

(3)

Two other high-temperature chemical

storage cycles are being studied by Westinghouse in the United States and KFA in West

Germany. In all three cycles, the primary

heat storage occurs in the dehydration and

pyrolysis of H2S O4

.

82 Several reactions have

also been proposed by Debini and Marchetti

(using CaBR2 and HgBr2

) Westinghouse (using a hybrid sulfuric acid process), General

Atomics (using an iodine-sulfur dioxide cycle), Schulten (using a methanol-sulfuric

acid process), the Lawrence Livermore Laboratory (using a zinc-selenium cycle), the Institute of Gas Technology (using iron chloride), and others.83 A major problem with all

of the reactions examined is low efficiencies

(typically 20 to 40 percent). In many cases,

the basic chemistry of the processes has not

been well established.

In addition to the calcium-bromide process described above, reactions using cesium,

tin, iodine-vanadium chloride, and iron chloride-oxide have been proposed. The calcium-bromide reaction appears to be the

most efficient, AlI require three or more

processes and considerable quantities of

process heat. 8485 The cost of such systems is

extremely difficult to estimate at present.

One preliminary study showed that a 47-percent efficient thermochemical-process plant

for converting solar-supplied heat into hydrogen would cost $25 per kW of thermal in82Data provided by ERDA, Off Ice of Conservation

8

‘E isenstadt and Cox, op c It , A Techrroeconornjc

Analysis of Large-Scale Thermochemical Production of

Hydrogen, (E PRI EM-287), December 1976, Pre//rm;nary

A5se55ment 0/ Econom/cs of Hydrogen Procfuctlon

From Lawrence Liverrnore Laboratory, ZnSe Thermocherr~lca/ Cyc/e, Un Ited E nglneers, September 1976

84R F Chao and K E Cox, “An Analysls of Hydrogen Produc tlon vIa C Iosed Cycle Schemes, ” Proceedings, THEME Conference, Mlaml Beach, Fla ,

S13 1 -S1 32 (March 1974), cited In E Isenstadt and Cox

a5Pangborn, op cit , p 174
64 ● Solar Technology to Today’s Energy Needs

put capacity .8’ Converting this to 1976 dollars and removing the contractors overhead

and profit, which will be added in later, this

cost is $26 per kW of thermal input capacity, or $57 per kw of hydrogen- production

capacity. This cost does not include the cost

of hydrogen storage tanks, which would cost

a great deal. A big central system could pipe

the hydrogen to gas customers in natural gas

pipelines, or store it in depleted natural gas

wells, but these options may not be available to the small onsite units. I n addition,

much work remains to be done on the systems, however, and it seems that the chemistry required will be too complex for any but

the largest “onsite” facilities being examined in this study.

SULPHUR DIOXIDE/SULPHUR TRIOXIDE

Some of these difficulties associated with

the methane system can be avoided in the

other simple chemical system which has received major interest—the

reaction. Its major advantage is that only

the oxygen cannot be stored as a liquid at

ambient pressure and temperatures; this results in a very substantial saving in the cost

of storing the material. The system has no

side reactions, and it requires relatively

small catalyst volumes.

Since the sulfur trioxide reaction reaches

completion at temperatures nearly 2000 F

higher than the methane/steam system, a receiver and reaction chamber must be made

out of ceramics or other material capable of

withstanding high temperatures. The development of such a receiver presents a major

problem. The system would also require relatively large heat exchangers at both the

collector site and in the system for reacting

the sulfur dioxide to generate heat. This

results from the high molecular weight of

the materials used and the necessity of condensing the products in the heat exchangers.

The sulfur system could also present corrosion problems since corrosive acids would

form if any water entered the system; the

safety problems associated with piping the

materials must also be examined.

Examining the chemicals in table Xl-6, it

appears that one of the most attractive materials for high-temperature storage would

be NH4H S 04

, since all of its reaction products can be stored as Iiquids at ambient temperature and since its reaction temperatures

are not as high as those required for the S03

system .87 Work has begun on this and a variety of other reactions, and it is clear that

not all possibilities have been explored.

The sulphur compounds used in this storage system could create environmental hazards if the equipment leaks or is not properly maintained. Accumulations of sulfurbased gasses can be highly toxic and may be

explosive under the right conditions.

Summary

The costs of several of the high-temperature thermal storage systems discussed in

this section are summarized in figure XI-21.

ELECTRIC STORAGE

All of the storage devices examined thus

far are designed to deliver heat which can

be either used directly to heat a building or

for some other purpose or to operate a heat

sw Hauz, et al,, Publication 72 TM P-1 5, General

Electrlc-TEMPO, Santa Barbara, Calif., April 1972,

cited in E isenstadt and Cox.

engine. It is also possible to store the electricity produced by heat-engine generators

or photovoltaic devices. EIectricity can be

“stored” directly in a loop of superconducting (zero-resistance) wire, and although research is being conducted on such devices,

a7Wentworth and Chen, op. cit
Ch. Xl Energy Storage ● 465

Figure XI-21 .— High-Temperature Thermal Storage Cost per kWht Versus

Storage Capacity

200

100

50

20

10

5

2

1.00

.50

.20

Note: The storage units would lose

only about 5Y0 of the energy

stored in the interval indicated.

.10

100 1000 104

Storage capacity (kWht)

105 10’
466 ● Solar Technology to Today’s Energy Needs

they are unlikely to play a significant role in

energy storage for some time. AlI other

forms of electric “storage” convert the electricity into mechanical or chemical energy

in such a way that electricity can be easily

removed.

MECHANICAL STORAGE DEVICES

The only large-scale electric storage systems in use today are pumped hydroelectric

storage facilities. A conventional installation consists of two lakes connected with a

device which is a combination pump and

turbine generator. Water is pumped into the

upper lake when energy is available to

charge the storage and is discharged

through the turbine generator when the

system is discharged. Standard hydroelectric facilities can provide storage since the

flow of water through turbines can be restricted during periods of low demand, in effect storing water in the dam’s lake for later

use.

Hydroelectric storage facilities are likely

to continue to be one of the least expensive

techniques for storing electricity, even if advanced electric storage systems of other

types are developed. Unfortunately, the

United States has already exploited a significant fraction of the most attractive sites for

hydroelectric facilities, and attempts to develop many of the remaining sites are likely

to face determined opposition on environmental grounds. A number of potential sites

are protected under the “Wild and Sceni c

Rivers Act” and other legislation. A pumped

hydroelectric facility is particularly unattractive from an environmental standpoint,

and the lakes created are difficult to use for

recreation. This is because the water levels

in lakes created in a pumped hydroelectric

system change significantly throughout the

day and the pumping continuously mixes

water from different parts of the lake.

It may be possible to greatly expand the

number of potential sites for pumped hydroelectric facilities by placing one of the storage reservoirs deep underground as llustrated in figure Xl-22. Such a facility could

be located wherever minable rock exists at

the required depths, but would cost considerably more than a standard hydroelectric

facility. Recent estimates of the cost of a

pumped hydroelectric facility capable of

producing 2,000 MWe for 10 hours range

from $270 to $350/kW. 88

Looking in another direction, it has been

found that a very large amount of potential

hydroelectric capacity can be found in the

numerous small dams which already exist

around the United States. The generating

capacity of existing small hydroelectric sites

could be expanded, and generators could be

added to a number of dams which currently

are used exclusively for other purposes, The

results of a preliminary survey of the opportunities presented by existing dams are

summarized in figure Xl-23 and table Xl-7.

The survey discovered that a generating

capacity of 26.6 GWe could be installed at

small dams (dams capable of producing less

than 5 MWe of power) and that these small

facilities could provide 159 billion kWh annually. This represented approximately half

of the new capacity identified. The extent to

which such dams couId be used for power

and storage cannot be determined without a

more detailed examination of the issue.

It must also be recognized that solar

energy systems will not be able to benefit

directly from most of the added hydroelectric capacity, since utilities will want to take

maximum advantage of new and existing hydroelectric facilities for storage and for

meeting peak demands. Solar equipment

could benefit indirectly to the extent that

the new facilities improve the ability of utilities to meet fluctuating demands. Mechanical storage of electricity can also be accomplished with flywheels by compressing gas in

underground caverns for use in Braxton cycle engines, and in other ways. These techniques have been adequately reviewed elsewhere.

“Frank M. Scott, “Underground Hydroelectric

Pumped Storage. A Practical Option,” Energy, Fall

1977, p 20.
Ch. XI Energy Storage . 467

Figure Xl-22.— An Isometric View of an Underground Pumped

Vent

house

Upper /

reservoir

Penstock shaft

Lower

reservoir

Tail race

‘ Access

building

Construction

and

ventilation

shaft

Manifold

Pens

tunnels and sucti

(Not to scale)

Storage Plant

Ground level —

SOURCE: Scott, Frank M. “Underground Hydroelectric Pumped Storage: A Practical Option” Energy Fall/1977 p. 20
468 . Solar Technology to Today’s Energy Needs

15

14

13

12

11

10

9

8

i

‘-- 7

6

5

A

3

2

1

0

Figure Xl-23.— Conventional Hydroelectric Capacity Potential at Existing Dams

36,418

35,661

\

SOURCE McDOnald. R J Pr[ncfipal lnV=tI@o~ (us .ArmY cows O! Efwmeers

Es!,mate of Na!lonal l+ydroeleclrtc Power POtentlal at Extst#ng Dams July 20 1977
Ch. Xl Energy Storage ● 469

Table XI-7.-Conventional Hydroelectric Capacity

Constructed and Potential at Existing Dams

——

Capacity Generation

(millions of (billions of

kW) kWh)

Developed . . . . . . . . . . . . 57.0 271.0

Under construction . . . . . 8.2 16.8

Total installed . . . . . . 65.2 287.8

Potential rehabilitation

of existing hydrodams 5.1 24.4

Potential expansion of

existing hydrodams . . . 15.9 29.8

Potential at existing nonhydro dams greater

than 5,000 kW . . . . . . . . 7.0 20.4

Potential at existing nonhydro dams less than

5,000 kW . . . . . . . . . . . . 26.6 84.7

Total potential . . . . . 54.6 159.3

Total (developed

and undeveloped). 119.8 447.1

SOURCE: McDonald, R J Principal Investigator (U.S. Army Corps of

Engineers Institute for Water Resources), “Estimate of National Hydroelectric Power Potential at Exlstlng Dams,” July

20, 1977

BATTERY STORAGE

Batteries are able to store electrical energy by using a variety of different reversible electro-chemical reactions. The electrical energy must be introduced and withdrawn from batteries as direct current, however, and a “power-conditioning” device

must be included in any battery system

which receives and produces alternating

current. Within large bounds, the cost of

batteries per unit of storage capacity is independent of the size of the system since

most batteries are built by combining a

large number of individual reacting cells.

Larger systems may benefit from some economies of scale because of savings due to

more efficient packing, lower building costs,

and possibly lower costs of power conditioning for larger systems, but a separate analysis on this point must be performed for

each type of battery. It is likely that there

will be an optimum size for each device.

Lead-acid batteries are the only devices

currently mass produced for storing large

amounts of electrical energy using electrochemical reactions. Systems as large as

5,000 kWh are currently used in diesel submarines. Batteries now on the market which

can be deeply discharged often enough to

be attractive for onsite or utility storage applications, however, are too expensive for

economic use by electric utilities. Extensive

work is being done to determine whether it

is possible to develop batteries suitable for

use in utility systems. Work is being done on

advanced lead-acid battery designs and on

several types of advanced batteries which it

is hoped will be less expensive than lead-
470 ● Solar Technology to Today’s Energy Needs

acid batteries in the long term. This work

has been thoroughly reviewed in several recent papers . 89 90 91 92

Lead-Acid Batteries

When voltage is applied to a lead-acid

battery, energy is stored by converting the

lead sulfate (PbSO4

) on the battery electrodes into a mixture of pure lead (Pb), lead

dioxide (PbO2

), and sulphuric acid (H2S 04);

the reaction is reversed when the battery is

discharged.

The current market for lead-acid batteries

capable of muItiple deep cycles is very Iimited and prices are high. (Automobile batteries cannot be used in power applications

since the full charge in such batteries cannot be withdrawn repeatedly without damaging the battery. ) “Houselighting battery

sets” are being manufactured for use with

windmills and remote generating plants.

Units capable of 2,000 deep cycles cost approximately $385/kWh.

93 94 Golf cart batteries sell for as little as $40/kWh, but are

only capable of about 350 cycles. Industrial

traction batteries, used in fork-lift trucks

and the like, have Iifetimes of nearly 2,000

cycles and are available for as little as

$80/kWh.

89An Assessment of Energy Storage Systems Suitable

for Use by E/ectric Uti/ities, Public Service Electric

and Gas Company under E PRI Project 225 and ERDA

Contract No E (11-1 ~2501, Vols. I & 11, july 1976.

‘“Near-Term Energy Storage Technologies: The LeadAcid Battery, a compilation of papers presented at the

ERDA-E PRI-ILERO Workshop, Dec. 18-19, 1975, EPRI

SR-33

91j R, Birk, The Lead-Acid Battery for E/ectric

Utilities: A Review and Analysis, presented at ERDAE PRI Lead-Acid Battery Workshop 11, Dec. 9,1976

‘*Ralph Whitaker and Jim Birk, “Storage Batter[es:

The Case and the Candidates, ” EPR/ journa/, October

1976, pp 6-13

“Prices quoted by Solar Wind Company, North

Orland, Maine The batteries are of Austrian manufacture and come in a clear polystyrene case with bu i It-in

pilot-ball charge indicators in each cell.

“All prices quoted are based on the battery capacity when discharged to rated depth-of- discharge

Unless otherwise stated, it is assumed that batteries

operate with 80-percent discharge in a typical cycle.

The Department of Energy asked several

battery manufacturers to estimate how

much it would cost to manufacture a battery capable of storing 5 megawatt-hours,

discharging in 10 hours, and lasting 500 to

1,000 cycles, using essentially off-the-shelf

components. The manufacturers’ responses

averaged about $93/kWh, but responses

varied from $41 to $138/kWh.95 This spread

reflects a range of battery capabilities. An

independent survey conducted by the Bechtel Corporation resulted in an estimate of

about $63/kWh.96

The industrial battery price of $80/kWh

will be used in further analysis to represent

“current” battery prices for community

systems.

While the range of prices encountered for

near-term batteries reflects the differing

specifications, production rates, etc., there

is rather remarkable agreement about what

batteries will cost in the intermediate term

when comparable assumptions are used. Table Xl-8 shows recent estimates of the price

and specifications of load-leveling batteries,

assuming a production rate of 1,000 MWh/yr

in a dedicated production facility. These estimates reflect a relatively rapid writeoff of

plant costs. Westinghouse has estimated97 a

selling price of $41.68/kWh by assuming vertical integration of lead production and battery manufacture, present battery technology, and more optimistic assumptions about

writeoff.

A major disadvantage of contemporary

lead-acid battery designs is their relatively

low storage capacity per unit weight. This is

due largely to the amount of lead used.

Lead-acid batteries have a theoretical “energy density” of about 0.175 kWh/kg, and

““A National Battery Energy Storage Test (BEST)

Facility Conceptual Design and Design and Cost

Estimate,” BEST Facility Study Project Team, EPRI

255, ERDA 31-109-38-2962, Technical Report 1, August

1975, p I 11-11

9’Bechtel Corporation, op clt

97 Study of the Manufacturing Costs of Lead-Acid

flatteries for Peaking Power, Final Report ,

Westinghouse Electric Corp , ERDA Contract No.

E(40-18}21 14, December 1976,
Ch. Xl Energy Storage 471

Table X1.8.—Economic Specifications (5-hr Battery)

——— . .— .

Specification C & D

a ESB Globe-Union Gould Westing -

houseb

Price ($/kWh)c . . . . . . . . . . . 55 56 58 5 4

d

49

Life (cycles at 77” F), ., . . 2,000 2,000 2,000 2,000 1,750 (95° F)

Price/cycle, ., . . . . . . ., . . . . 2.7 2,8 2.9 2.7 2.8

Efficiency (%)e . . ., ., 73 76 72 70 68

Replacement price ($/kWhr) 40 32 38 25 34

O&M cost (mills/ kWhr ) 0.28 0.18 — — —

—- —.-

aea~ed upon B50,0 depth Of d IsCharge to achieve 2,000 cycles Instead of 95°. of discharge to achieve 1,250 cycles

at a price of $49/ kWhr (to be discussed)

bDoes no[ reflect raw ~aterlals Integration and market optimism Included by Westinghouse (to be discussed)

cAssumes 25c / lb lead

‘Installed cost

el ncl udes Conversion eff Iclency Of 9000

SOURCE James R Blrk, “The Lead-Acid Battery for Electrlc Utlllt}es A Review and Analysls “presented at the

ERDA / EPRI Lead-Acid Battery Workshop 11, Dec 9, 1976

thus a perfect battery would weigh about

12,6 pounds per kWh. Commercial batteries

weigh more than this because of design inefficiencies and the need to provide packaging for the active materials Commercial

lead-acid systems weigh about 100 pounds

per kWh of storage capacity, of which 60 to

80 pounds is lead The cost of this rather

substantiaI quantity of lead imposes a practical lower limit on the price of lead-acid

batteries

In 1975, when ERDA asked three of the

largest battery manufacturers in the United

States to design the lowest cost battery for

utility applications, the estimates of material costs ranged from $24 to $34/kWh. 98

(The range is much smaller if allowance is

made for the differing Iifetimes of the designs. ) Very high production volumes would

be required before the price of the complete

battery would approach this minimum

material cost.

The Axel Johnson Institute for industrial

Research in Sweden has proposed a novel

technique for reducing lead requirements by

using aluminum electrodes covered with a

lead coating. The device is currently being

tested by EPRI.99

The current U.S. production rate of lead

could support all foreseeable needs of onsite electric systems and should be able to

support the development of a nationwide

battery system used for utility peak shaving

(although the price of lead would undoubtedly increase if a very large demand developed). Present U.S. domestic lead consumption is about 600,000 tons per year, and our

reserves are estimated at 40 miIIion tons

(World production is approximately 3.6

mill ion tons and world reserves 141 mill ion

tons.)

1oo Thus, at present energy densities,

current production rates could provide 15 to

20 million kWh of storage per year or

enough to provide 4,000 to 5,000 MWe for 4

hours every day. At this rate of production,

therefore, it would take 10 years to develop

a battery system capable of meeting 10 percent of U.S. electricity demand for 4 hours

“A C Slrnon and S M Cauldar, “The Lead-Aci d

f3a t tery, Proceeding~, Symposium and Workshop on

Advanced F3attery Resear( h and Design, Argonne Natlon~l Ldbordtory (AN L-76-8), Nldrc h 1976

‘“OM/ner.?l\ \earbooA, U S Department of the lnterlor, [3u reau of JMI ne~, 1973
472 ● Solar Technology to Today’s Energy Needs

per day. The lead used in the batteries is not

consumed in the storage process, and after

the initial investment is made, the material

can be recycled indefinitely.

An ordinary automobile battery will last 3

to 5 years, undergoing extremely shallow

cycles several times a day, but would be

capable of only 150 to 250 deep discharges.

The electrodes in batteries used in golf

carts, industrial forklifts, etc., are usually 2

or 3 times as thick as those used in car batteries and are typically capable of 300 to

500 deep cycles. Batteries capable of discharging 2,000 times are currently available

and this has become a design objective for

utiIity storage batteries.

A practical limit to the depth of discharge

which can be obtained from a given battery

design can be obtained by watching the battery’s voltage. This voltage drops slowly during discharge and then begins to f al I sharply.

If the battery is discharged beyond this

point, its life is shortened substantially.

ENVIRONMENTAL AND SAFETY PROBLEMS

Lead-acid batteries produce potentially

hazardous gasses, such as hydrogen, arsine

(AsH,), and stibine (SbH3

) when they are

cycled. Hydrogen released in the atmosphere has no effect on air quality or human

health, but is highly flammable and explosive in concentrations above 3 percent. This

danger can be eliminated by placing batteries in well-ventilated compartments.

Arsine and stibine are toxic, colorless,

gaseous compounds which form during the

required, periodic, high-voltage charging of

lead-acid batteries. For example, the recommended threshold Iimit values for arsine and

stibine in workroom air are 0.05 ppm (0.2

mg/m

3

) and 0.1 ppm (0.5 mg/m3), respective

Iy.lO1 Whether these levels will be exceeded

when charging lead-acid batteries for home

‘“’’’ Report on an Engineering Study of a 20 MWh

Lead-Acid Battery Energy Storage Demonstration

Plant,” for Argonne National Laboratory under Contract No. 31-109-38-2962, by Bechtel Corporation, October 1975, p. 5-5.

energy storage is presently unknown. The

recognition of the possible adverse environmental impact of arsine and stibine and implementation of appropriate safeguards–

proper battery placement and ventilation –

reduces the risk of harm from these gasses.

Advanced Batteries

Three basic categories of advanced systems are under exam i nation:

1.

2.

3.

Aqueous or water-based systems which

operate with electrodes surrounded by

a liquid electrolyte, as do lead-acid

systems.

Nonaqueous high-temperature systems,

which use a nonaqueous material to

conduct ions needed to complete the

electrochemical reaction.

“RED OX” (reduction/oxidation) devices

which reduce aqueous solutions to

store energy. (REDOX batteries are

“aqueous,” but they are usually considered separately. )

Table Xl-9 summarizes the characteristics

of several advanced battery designs.

AQUEOUS BATTERIES

Zinc Chloride

Zinc-chloride batteries are aqueous de

vices which can store electrical energy in

aqueous chemical solutions at ambient temperature. Research on this battery is underway in a joint venture of Gulf Western Industries and the Occidental Petroleum Corporation. Small (50 kWh) units have been

tested at Argonne National Laboratory, and

it is expected that a 10 MWh battery will be

tested in a realistic utility environment by

1980.

The small experimental batteries now being produced cost approximately $2000 a

kilowatt hour, but when the system reaches

production stages, cost is expected to be

reduced to $40 to $50. This is more expensive than projections for lithium or sodium

battery systems, but this cost is offset to
,.

.

Table X1.9.—Load-Leveling Batteries: Candidates and Characteristics; Developers and Demonstration Dates

Lead acid (Pb/Pb02) 2030 110 11 075 25 10 -15

Sodium sulfur

(Na / S) 300350 360 70 2 5 85 75

Sodium-antimony

trichloride

(NA SbCl3) 200 350 50 20 80-90 25

Litium-metal sulfide

400450 430 85 35 80 30

Zinc chlorine

(Xn/C l

2) 50 210 45 1 0 100 40-50 b

Z[nc-bromine

(Zn / Br2) 30-60 195 40 15 90 30

Hydrogen-chlorine

( H2 / C l

2 ) 30-60 450 50 0 3

95 300

REDOX am bient — 40d — 90 40-60

Iron REDOX ambient — 38 2 6

aAl SCJ known as Utw!zatlon of acllve m.ater, als

b5 n, rate

‘GE c al, dales fof IZ.I,IZI

a[whllstre 0! sol. t,onl

SOURCES EPRI Journal and K.n w Klund91 Battery Branch Of f#ce of Conservation EROA

850

049

235

4 27

Theor - 0.59c

Practical - 0.84

Theor - 1.56

Practical - 1.65

20

$3-$10

$1

>20

0 5

002

1 0

1.7

01

001

005

2,000

400

175

1000

2.000

50

200

>1 ,000

Lead

Antimony

Lithium

Ruthenium

(catalyst)

None

Platinum

Ruthenium

(catalyst)

None

None

Gould Inc ESB Inc C&D

Batteries Globe-Union

Inc.: K.W. Battery Co

General Electric Co Dow

Chemical Co Ford Motor

c o

ESB Inc

Atomics International DIV

RockwelI International

Corp.: Argonne National

Laboratory

Energy Development Associates

Exxon Gould GE

GE, BNL

NASA-Lewis

G E L

1979 1981 83

1981 82

1981 82

1980

1980

1983 — Post 1985

1983 . Post 198’3

1984 1986

1980

1988

I

I

\
474 ● Solar Technology to Today’s Energy Needs

some extent by the fact that zinc-chloride

batteries produce a constant voltage and

equipment necessary to convert the current

to a.c. is cheaper than other systems, resulting in an overall competitive price. Zincchloride batteries are capable of operating

at ambient temperatures, but require a complex plumbing system for circulating the

electrolyte and controlling the temperature

of the system. ’02 ’

03 The presence of chlorine

gases could create an environmental problem if used in onsite systems.

Zinc Bromide

The zinc-bromide battery is another aqueous device being developed primarily for

utiIity load leveling and electric automobiles. Early work on these batteries was done

by the G.E.L. Corporation of Durham, N.C.

Devices developed by the General Electric

Corporation have operated for more than

2,000 cycles of 2.5 hours discharges. ’04

Researchers at G.E. believe that batteries

based on this concept, capable of 65 to 80

percent efficiencies, should cost no more

than $17 to $26/kWh (excluding the cost of

pumps, controls, and marketing). The major

problem is the development of a low-cost

and reliable membrane. Imperfect membranes lead to a “self-discharge.” In the

most recent G, E. designs, the cell discharges

at about 0.1 percent per hour.

One potentialIy serious problem with zinc

bromide is the caustic nature of the bromine

solution. Containment of this material can

be expensive and great care must be taken

to ensure that this powerful chemical is

properly contained.

HIGH-TEMPERATURE BATTERIES

Sodium/Sulfur

Sodium/sulfur batteries, under developments by the Ford Motor Company, use ac-

‘(l’N Yao and j .R Blrk, op cit.

“] ‘t3echtel Corp , op cit.

‘

(

”F G Will, “The Zinc-Bromide Battery: Possible

Candidate for E Iectric Vehicles and Load Level ing, ”

Proceedings, 12th IECEC Conference, 1977, p 250.

tive materials which are inexpensive and

widely available. Most of the development

work on this battery has centered on a solid

electrolyte material called “beta-alumina”

(an alloy made of sodium, aluminum, and

oxygen), 05 and the electrolyte costs considerably more than the active materials today. ’”’ Small 10-to-15 watt sodium/sulfur

celIs are now being run in excess of 3,000

cycles, and Ford hopes to test a 5-to-10

MWh battery in late 1981. A second sodium/sulfur concept is being developed by

Dow Chemical, and is about 2 years behind

the Ford research. Both systems still cost

some $3,000 a kilowatt hour, but projections

are that the Ford system will be reduced to

$30 by 1985-87, while Dow suggests that a

$24.50 cost can be attained perhaps a year

later from its system. G.E. and EPRI spent

about $3.5 million developing this system

between 1967 and 1976, and expect to spend

about $3.5 milIion in FY 78.

Systems have been demonstrated which

are capable of 90-percent discharge and 77

percent-efficiencies. ’07 The major development problem remains the beta-alumina

electrolyte. Poor quality material tends to

crack and degrade and seals have been unreliable, Another issue, identified as a problem by G.E,, is the difficulty which may be

encountered in scaling the units up to a size

where they can be used in large central utility applications. It is expected that large batteries will be constructed from units of 10 to

100 kWh.‘08

Lithium-Metal Sulfides

Lithium-metal sulfide batteries are being

examined primarily by Argonne National

Laboratories under a DOE contract. Argonne is now making 150 W/h cells capable

““N P Yao and J R Birk, op cit , p 1107.

IObArthur L Robinson, “Advanced Storage Batteries Progress But Not E lectrlfytng, ” Science, May 7,

1976, p 543

‘07S. P Mitoff, et al , “Recent Progress In the

Development of Sodium Sulphur Battery for Utility

Applications, ” Proceedings, 12th I ECEC Conference,

1977

‘O’S P Mltoff, Op. clt
Ch. X/ Energy Storage 475

of 500 deep cycles. I n 1982, a 5-to-1 O MWh

cell module is scheduled to be tested in

Argonne’s Battery Energy Storage Test

(BEST) facility. Argonne foresees a cost of

$29.16 per kWh at full production in

1985-87. Like sodium/sulfur batteries, lithium-metal sulfide devices now cost about

$3,000 a kwh to produce experimentally

and in small working applications.

Both the sodium/sulfur and the lithiummetal sulfide batteries operate at temperatures above 300 “C, and the combination of

high temperatures and reactive materials requires hermetic sealing. 109 There are accompanying seal problems. Questions have been

raised about the safety of using the sodium/sulfur system in large numbers unless

stringent precautions are taken to protect

against a rupture of the containment vessel.

Since the lithium battery uses two metals,

the chemical reaction caused by a rupture

would not be as serious as it would in a

sodium cell, which uses two Iiquids.

Both lithium and sodium are flammable

and, under some conditions, explosive. 1

0

The use of lithium and sodium batteries,

therefore, must include careful provision for

fire and explosion containment.

REDOX BATTERIES

The REDOX battery presents a tantalizing

opportunity for electric storage since devices based on the design may be able t o

store energy in tanks of inexpensive chemicals; storage costs couId be $10/kWh or less.

The problem which has plagued the development of these systems for many years is

the need for a semipermeable membrane

with some rather remarkable properties. The

need for a sophisticated membrane could be

eliminated, however, if an iron-REDOX design is perfected.

’09 Herbert P. Silverman, Lynn S. Marcoux, and Eddie T. See, TRW, Inc , “Development Program for

Solld E Iectrolyte Batteries, ” Final Report for EPRI,

EM-226, September 1976

1 I°Chemlcal Rubber Company, Handbook of

Chemistry and Physics, 54th Edltlon, 1973-74, pp B-19,

B-31

In a standard REDOX battery, the two

storage tanks (called the “catholyte reservoir” and the “anolyte reservoir” in the diagram) contain different chemicals. In one

design which has received recent attention,

the tank connected to the positive terminal

contains a solution of F e

+2 and Fe+ 3 ions,

and the tank connected to the negative terminal contains a solution of Ti + 3 and Ti

+ 4

ions. When the battery is completely discharged, the one tank is filled with FeCl2 and

the other with TiCl4

. When the battery is being charged, negatively charged chlorine

ions drift across the semipermeable membrane and combine with FeCl 2

, producing

FeC l3 and giving up the extra negative

charge to the positive terminal. On the other

side of the membrane, chlorine ions are released when TiC l4 forms TiCl3

, taking an

electron from the negative electrode. The

electric current from the positive to the

negative electrode is matched by the flow of

chlorine ions across the membrane. It is important that the membrane be able to pass

chlorine ions with minimal resistance, but

not allow either the iron or the titanium to

pass. If iron or titanium leaks through the

membrane, the performance of the device is

gradually degraded. NASA-Lewis has been

working on systems based on this design for

a number of years, and it is hoped that a battery suitable for demonstration in utility applications will be available by 1985.

Iron REDOX

The iron-REDOX battery being developed

by the G.E.L. Corporation operates on much

the same principle as the REDOX system just

described, but uses the same chemical a t

both electrodes, thereby greatly simplifying

the requirements placed on the membrane. 112 The basic components of an ironREDOX battery system are illustrated in

figure Xl-24.

When the iron-REDOX system is completely discharged, the storage tanks are

“ ‘K. W. Klunder, Office of Conservation, ERDA,

private communication

1

12The C E L. Corporation, Durham, N C , Per -

formance Status, January 1977
476 ● Solar Technology to Today’s Energy Needs

‘ “Dr. R Zito, President, the G.E. L Corporation,

private communication, September 1977.

by resistive heating. With design improvements it may be possible to achieve overall

efficiencies of 80 to 85 percent with

moderate discharge rates. The system is not

damaged by deep discharges.

The reaction chamber with its membrane

will account for the bulk of the cost of the

iron-REDOX system – the chemicals and the

tanks needed to store them will probably

cost less than $2/kWh. The cost of this reaction chamber is a direct function of the area

of membrane required. G. E. L. estimates that

the graphite electrodes they are now using

can store about 1 amp-hour per square inch

of electrode surface. After this thickness has

been deposited, the deposited iron becomes

uneven and physically unstable. If a large

area is allowed per unit of power delivered,

the system is more efficient but costs per

kilowatt increase. The cost of reactors capable of delivering different amounts of power

per unit of membrane surface is shown in table XI-10. An electric storage system deFigure Xl-24.— lron”REDOX Battery Structure and Plumbing Diagram

Catholyte

ir

SOURCE: GEL, Inc , Durham, N C
Ch. Xl Energy Storage ● 477

Table XI-10.— Loss Mechanisms of

iron-REDOX Batteries

Loss factors

Loss mechanisms Percent at Percent at

0.10 A / in2

0.4 A / in2

H 2 evolution . . ., . . . . . 1-2 2.3

pH regeneration . . . . ., 1-2 2-3

Fe + 3 membrane diffusion . 2-3 0.5-2

Joule heating

—electrolyte 2-4 6-14

—thru membrane . . . . - o - o

Polarization effects ., . . 14-20 14-20

Fluid pumping, . . . . . . . ‘1 - 1

Fluid manifold conduction -1-2 -1-2

Total loss. . . . . . . . . . . . . 22-34 26.5-45

Reactor cost . . . . . . . . . . . . . $68/ kW $18/kW

SOURCE The G E L Corporation, Durham, N C., September 1977

signed for use in a solar energy application

may require a device capable of storing a

large amount of energy for periods of 10 to

20 days, but there would be no need to discharge the entire device over a short period.

The REDOX device would appear to be well

suited for such an application.

The devices will probably not show significant economies of scale until systems of

more than a few hundred kwh of storage

capacity are constructed.

G.E.L. is presently constructing a 2.2 MWh

iron-REDOX battery system with a peak output of 250 kW for use in the Mississippi

County Community College total solar energy system. This DOE-sponsored project

should be operating by late 1979. The storage system will consist of 24 reactor modules rated at 11 kW. Each module will contain 130 to 150 bipolar electrodes and will

measure approximately 120 x 60 x 240 cm

(2 ‘ x 4 ‘ x 8 ‘). The entire system will require

60,000 to 80,000 liters (1 5,000 to 20,000

gallons) of electrolyte. A model of the system is shown in figure Xl-25. Electrodes and

membranes for the system have been developed for reproduction with acceptable electrical and mechanical characteristics, but

improvements can be expected as the design

matures. To date, no chemical or mechanical problems have been encountered which

would cast doubt on the ultimate practicality of the device. However, firm conclusions

are not possible until information becomes

available from a demonstration of the fullscale system.

POWER CONDITIONERS

Design Alternatives

Most battery storage systems will require

some kind of “power-conditioning” system

to supervise their connection with sources

of charging energy and with the loads met

whiIe discharging.

This equipment can serve four functions:

1

2

3

4

Regulate the rate at which a battery is

charged and discharged to protect the

battery and extend its useful life;

Serve as a switching system, and determine whether the loads will be met directly from the onsite generating system, from storage, from the utility, or

from some combination of these (in

some cases it can also allow the storage

to be charged from the utility);

Rectify alternating current received

from the onsite generator or from the

utiIity so that this energy can be used to

charge the battery; and

Invert the direct current produced by

the battery or by the onsite generating

equipment, creating alternating current

whose voltage and frequency meet acceptable standards of uniformity.

A system which can perform all of these

functions is illustrated in figure Xl-26. Not

alI devices will be as complex as the one

shown, and designs wilI differ greatly from

one application to another.

The most important design decision is

whether to use an inverter. These devices

are by far the most complex elements of a

power-conditioning system and represent 85

to 95 percent of the cost of a typical power

conditioner. Inverters would not be needed
478 ● Solar Technology to Today’s Energy Needs

Figure Xl-25.— Model of iron-REDOX Battery Facility

. . . . ..* . . .-. .*X-. .K?. -. . . . . ..- .... .s. ss .

SOURCE: G. E, L.. Inc
Ch. Xl Energy Storage 479

Figure XI-26.—The Elements of a Power Conditioning System

DC Loads

Battery

Interface

I

Interface

I

AC Loads

if local loads could be met by direct current,

but these savings could be largely offset by

the costs of converting a residence or industry to d.c. operation. A quantitative assessment of this issue is beyond the scope of the

current study, but it is possible to outline

the major factors which must be considered

If conversion to a d.c, system is contemplated:

Over two-thirds of the power required

in a typical residence is used in equipment which could easily be converted

to d.c. operation. Incandescent lights,

heaters, stoves, heating elements i n

driers, etc., could all operate with

direct current without major difficulty.

The only devices requiring a.c. are

fluorescent lights, systems with electric

motors, and electronic devices such as

televisions, radios, and the like. Most of

these appliances are currently available

in d.c. versions, however, although

some are more costly than their a.c.

equivalents. A complete Iine of residential d.c appliances is available for

mobiIe homes.

●

It

Direct current systems would require

more expensive switches and fuses, The

cost of wiring would be higher if lowvoltage d.c. were used,

should also be recognized that a d.c,

system which relies on the utiIity grid to provide backup wilI need a rectifier. (Most inverters can rectify as welI as invert and so

would not require separate rectifying equipmerit. ) Rectifiers tend to cost about 30 percent as much as inverters of equivalent

power ratings.

A typical inverter can provide some kind

of fauIt or short-circuit protection and can

provide a.c, synchronized with the utility

grid. The cost, design, and performance of

inverters vary greatly and are strongly dependent on the quality of the a.c current required. Systems using grid backup wilI clearly be required to provide a well-filtered output which matches the grid in frequency and

‘“laclllty Systems E nglneerlng Corporation, 5/?oPPIng Center App/icat/errs of Photovo/ta/c So/dr Power

Sys(ems, ERDA Contract (1 1-1 ~.2748, 1976
480 Solar Technology to Today’s Energy Needs

phase. Performance is usually specified in

terms of the voltage control, and the harmonic content of the voltage produced.

Older units frequently were nothing more

than a d.c. motor which drove an a.c. generator, but most modern devices use solidstate components based on silicon-controlled rectifiers. The solid-state devices are

usually more reliable and require less maintenance. Most of these systems are “line

commutated” in that they rely on utility

power to establish the phase and frequency

of their a.c. generation. Devices operating

independently of grid power (self-commutated systems) are also available, but are

more expensive.

Interest in developing inverters of various

sizes has come from a variety of places.

Small inverters have been developed for

military applications, for smalI onsite generating plants (using windmills and conventional power sources), etc. Larger devices

are available from suppliers of interruptible

power supplies which are used in hospitals,

computer centers, and other installations

which cannot afford to lose power when

grid electricity is unavailable. Much larger

units are in use and being developed for d.c.

transmission Iines.

The design of interface and regulator systems is quite straightforward and systems

are available in a variety of sizes. The complexity and cost of the system will depend

strongly on the speed with which the system

must shift from one power source to

another, and on the system design.

System Performance

The efficiency of modern solid-state inverters is in the range of 92 to 95 percent

when the devices are operating at more than

about 25 percent of peak capacity. Below

this point, the efficiency falls off quite

sharply since a fixed amount of energy is required even at zero loads. Figure Xl-27 illustrates the part-load efficiency of a typical

Figure Xl-27.— Efficiency of a Solid-State

Inverter as a Function of Load

/

v 1 1 1 1 I

20 40 60 80 100

Operating point (0/~ of full load)

SOURCE: MERADCOM, DoD
Ch. Xl Energy Storage 481

sol id-state inverter. The mechanical inverter

systems mentioned earlier are typically less

efficient than the sol id-state units.

The overall operating efficiency of inverters in small systems will probably be lower

than the efficiency of inverters in large systems because there is less load diversity in

the smaller systems. This can be expected to

result in more operation at partial load.

Voltage regulators are quite efficient at

all power levels; typical systems are 98-

percent efficient. 115

BATTERY SYSTEM COSTS

Since there is considerable disagreement

about the future price of batteries and supporting equipment for onsite storage systems, cost estimates for battery storage systems wilI be given in four categories:

1. A near-term price, reflecting the costs

of devices which could be purchased in

1976.

1

‘‘Bechtel Corporation, Energy Storage and Power

Conditioning Aspects of Photovo/taic So/ar Power

Systems, prepared for Spectrolab, I nc , under Subcontract No 66725, October 1975.

2

3

4.

An estimate based on present estimates

of the cost of lead-acid batteries and inverters produced in large numbers

(1,000 MWh/yr) for distributed storage

applications.

An advanced-concept estimate of future prices which assumes that inexpensive, advanced battery systems such as

sodium/sulfur or lithium-metal sulfide

are successfully developed. This price

could also apply to very large contract

or Government purchases, where sales

overhead couId be reduced.

A very low-cost estimate which assumes

that low-cost advanced-concept systems such as iron-REDOX are successfully developed.

The results of these estimates are summarized in table Xl-11 and figure Xl-28.

The cost of a battery storage system consists of three major components: the cost of

the battery itself; the cost of the power-conditioning system; and the remaining cost

which includes instalIation and the space required to house the system. The cost of each

component is treated separately,
. —

Table Xl-1 1 .—System Cost Estimates for Near-, Intermediate., and Lena-Term

(Including 25-Percent Off)

—

Llfetlme (deep cycles )

0 & M cost (mills/kWh discharged)

Replacement cost (% of original)

Assumed discharge t I me (hours)

First costs

(1) Commercial and multlfam{ly

residentIal systems

Battery cost ($/ kWh)

BuIIding and other costsa

($/kWh )

Power-cond!tlonIng costs b

($/kW )

(2) Home systems

Battery costs ($/kWh)

BuIIdIng and other costs a

($/kwh )

Power-condItIonInq costs b

($/kW )

— —

Present market prices

2000

028

85

5

Present technology

wtth mass production

2000

028

60

5

Advanced concept or Long-term

advanced Iead-acid tech- iron-REDOX

nology wIth Iarqe firm contracts (e.g., GSA) 1990-2000

2000

(O 287)

100

5

2000

(c)

100

10
Ch. Xl Energy Storage . 483

Figure Xl-28.— Power-Conditioning Cost Versus Power

1000

0

50

20

~ 200 ---- -

x

0.1

1 KW

1

1 MW

100 1000

Rated power (kW)

100,00 0 1,000,000

Below 10kW this data represents catalog prices and quotes for commercialIy available units

The unit at $10/kW (3kW) provides square wave output. The prices between 10 kW and 25 MW are prices for uninterruptible power suppIies less batteries which

are generalIy more sophisticated t h an wiII be required for onsite electric systems

The data for higher power levels represent projected prices for utility load-Ievellng systems

—The solid line segments represent prices for a single manufacturer as a function of size

—– “Gemini Synchronous 8 kW Inserter, ” Windworks, P O Box 329, Mukwango. Wis

x Prices for current-fed inverter systems from Peter Wood. AC/DC power Conditioning and Control for Advanced Conversion and Storage Technology EPRI

390-1-1 (1975) The lower price IS for a Iine commutated system hiqher price IS for a comparable Isolated system
Chapter Xl

APPENDIXES
Appendix XI=A

A Technique for Estimating the

Allowable Cost of Storage Devices

Computing the amount which can be

spent on storage equipment requires a careful comparison of the Iife-cycle costs of systems with and without storage devices. It is

possible, however, to compute the approximate amount which can be spent on storage with the following simple algorithm:

the installed cost o f storage

capacity (in $/kWh)

the average number of storage

cycles per year

the fraction of the storage capacity

used in an average cycle

the effective cost of capital (see

chapter IX)

the cost of energy available when

storage is discharged ($/kWh)

E C =

M =

If the

the cost of energy available for

charging storage ($/kWh)

the efficiency o f the storage

equipment

the average annual operating cost

of the storage device ($/kWh of

energy stored)

storage is not owned by the utility,

then the costs E C and Ed represent the rates

charged for electricity during peak and offpeak periods. If the systems are owned by a

utility, EC would represent the cost of energy

provided by a baseload plant used to charge

storage and Ed would represent the cost of

energy provided by a peaking plant. The

allowable cost of storage calculated in this

way is iIlustrated for a variety of different

assumptions in figure Xl-A-1.

Figure Xl-A-1.– Permissible Cost of Storage Equipment as a Function

of Energy Prices During Storage Charge and Discharge

Batteries:

intermediate term

Pumped hydroelectric

Brick storage onslle

Low temperature Thermal

storage

487
A perfect thermal-storage system would

return all of the energy supplied to it at the

temperature at which the energy was originalIy supplied. I n real systems, of course,

energy is lost through the containers and the

transport system, and the temperatures of

fluids which discharge the storage are lower

than those used to “charge” the storage with

thermal energy. This temperature reduction

results not only from a net loss of energy to

the surroundings, but also from the mixing

of hot and cold fluids in the storage vessel

(if a single tank is used), unless stratification

is achieved, and from the temperature difference which must be maintained across

any heat exchangers which are employed.

One advantage of chemical storage systems is that the products of the reactions

can usually be stored at ambient temperatures. In chemical systems, however, temperature losses are the necessary result of

the fact that reversible reactions must operate with the forward reaction occurring at a

temperature different from the reverse reaction. Energy is also lost during the process of

cooling the hot chemicals emerging from

the high-temperature reaction chambers

down to ambient temperature. Some chemical reactions also require the addition of

“process heat” to stimulate intermediate

processes, and this heat requirement lowers

the overall “efficiency” of the storage process.

The significance of energy lost through insulation, parasitic loads due to pumps, process heat, etc., is clear. This is energy which

cannot be recovered for usefuI work. On the

other hand, the significance of storage temperature reductions which do not result in a

net loss of energy requires more explanation: 1 ) heat engines are more efficient at

high temperatures, and 2) the performance

of solar collectors decreases as the exit temperature of fluids produced by the collectors increases; thus collector performance is

maximized if the storage system can be

488

Appendix Xl-B

Analysis of Performance —

charged from the collectors at a temperature close to the temperature at which the

fluids will ultimately be used. In general,

systems which use the stored heat only for

space heating and domestic hot water will

not be as sensitive to temperature degradation as systems which generate electricity or

which drive air-conditioning systems directIy, but size and cost of even simple systems

can be reduced if the temperatures can be

kept high.

The designs chosen will depend crucially

on the economics of the system. Insulation

should be added until the incremental value

of the energy saved by insulation equals the

incremental cost of adding insulation, SimiIarly, the sophistication of systems designed

to maintain temperatures at constant levels

should be increased until the incremental

value of the energy provided by these systems is less than the incremental investment

needed to prevent the additional drop in

temperature.

STORAGE TEMPERATURE LOSS AND

HEAT ENGINE EFFICIENCY

In the immediately foIlowing analysis,

losses through insulation and temperature

drops across heat exchangers are ignored for

simplicity; they are included later. A detailed analysis of the effect of heat exchangers is contained in appendix A of

Bramlette. 1

The performance of heat engines can be

approximated by assuming that their mechanical or electrical output is some fraction (fe

) of their ideal Carnot efficiency.

Q out = fe Q ln (1- TC / Th )

(constant-temperature storage or two-tank system)

where QOut is the mechanical or electrical

energy generated by the heat engine, Q, n

I T T Bramlette, et al (Sandla I-a boratorles, Livermore), Survey of E//gh- Temperature Therma/ Energy

Storage, SAN D75-8063, March 1976
Appendix XI-B ● 4 8 9

was the energy originalIy sent to the storage,

T c is the temperature at which heat is rejected from the engine, Th is the temperature at which energy is sent to the heat

engine (also the temperature of the storage

medium), and T C and Th are absolute temperatures.

drops from Th to Th during discharge because of mixing or other effects, the energy

produced by the heat engine will be given

by:

L

and the enthalpy change associated with the

i

th phase change. Cp is the specific heat. The

specific heat is assumed to be constant for

all temperatures in this simple approximation.

In the case of a thermochemical reaction,

it is assumed that the reaction proceeds to

95-percent completion at a temperature Th

in the forward direction (in the solar collector), and proceeds to 95-percent completion

at

at

a temperature Th in the reverse direction

the user site. In this case:

It is now possible to define a uniform

figure of merit or “temperature efficiency”

techniques used with heat engines, It will

simply be the ratio of Qout for the technique

in question to Qout for a constant-tern perature storage system.

—————. (phase change with

perfect mixing)
490 Solar Technology to Today’s Energy Needs

The average efficiency of a heat engine

used with thermal storage is just:

ture Th

. Note that the heat engine will operate more efficiently than this average figure

when the storage is fully charged and the

“temperature efficiency” is not the same as

“round-trip storage efficiency” (QOut / Qln),

which is the ratio of the amount of heat

which can be recovered from a fulIy charged

system divided by the amount of heat which

is required to charge it. “Round- trip storage

efficiency” affects al I energy storage systems, while “temperature efficiency” is of

concern primarily for systems which drive

heat engines from stored heat. While a temperature drop sometimes signals a loss of

thermal energy, the “temperature efficiency” is a measure of how the engine performance is reduced as a result of heat being

delivered at a lower temperature, and has

nothing to do with how much energy was

first pumped into storage or how much subsequently leaked out.

SENSIBLE- AND LATENT-HEAT

STORAGE LOSSES

In storage systems using sensible and latent heat there are three primary loss

mechanisms: losses through the insulation;

temperature degradation in heat exchangers; and temperature degradation due to

mixing.

In all of the direct thermal-storage applications considered, it will be assumed that

the storage vessels are cylindrical with a

radius R and a height L which is equal to 4R.

Losses Through the Insulation

The losses from such a tank will, in general, depend on the thickness (ti

) and conductivity (k) of the insulation and the heat transfer coefficient (h) giving the conductive,

convective, and radiative losses of the outer

insulation surface to the air or ground. The

heat loss rate (Q) from the cylinder just

described would be approximately:

where Ts is the average temperature of the

storage material and Ta is the ambient temperature; RO is the radius of the cylinder with

insulation, and RI is the radius inside the insulation.

This equation can be simplified in most

cases of practical interest by assuming that

the thickness of insulation (t,) is small compared to RO [i. e.: (RO

-Ri) is much less than R,]

and that the quantity k/h is small compared

with t,. This last condition is equivalent to

an assumption that the air or earth surrounding the tank provides no insulation, and is,

therefore, a conservative assumption. Figure

Xl- B-1 shows that most common insulations

have k less than 0.05 Btu/hr fto

F. h will range

between the value for air with free convection (l-5 Btu/hr ft2oF) to that of water with

forced convection (50 to 100 Btu/hr ft2oF). ’

Figure Xl- B-1 .—Thermal Conductivity of

Insulation

0.7 ~ /

,

O 100 200 300 400 500 600 700 800

Mean temperature, Fahrenheit

SOURCES:

1. ASHR.4E H8ndbook of Fundamentals. 1972, Page293.

2. “l%amglass Insulation” Brochure FI-132 (REV). Pittsburgh COrning Corp., April 1975.

‘F T Krelth, Prlrtclp/es of Heat Transfer, second edition, 1965, p 15
Appendix XI-B 491

It can be seen that k/h is small for either

assumption. I n the remainder of this discussion, a cylindrical storage container with

length L = 4R is assumed, unless stated

otherwise. With the assumptions tj/R<< 1

and ti<< k/h, the heat flow Q from the

cylinder can be approximated as follows: Earth Insulation

In practice, the soil itself will provide

some insulation for a buried tank. The insulating properties of the soil will depend

strongly on local conditions, in particular,

ground water flows, The heat conductivity

of soil, for example, varies from 0.1 Btu/hr

fto

F for dry sand or soil to 2 for wet sand or

soil.

3 Assuming that the storage tank is a

simple hemisphere, it can be shown that the

heat leaving through the earth when equilibby:4

As noted earlier, in an actual design, the

insulation thickness wouId be chosen so that

the marginal cost of adding additional insulation wouId be equal to the marginal cost

of energy saved by adding this insuIation.

For simplicity, the Insulation used in the

calculations which follow is based on t h e

premise that only 5 percent of the stored

energy wiII be lost during the desired storage

interval of Ø hours (Ø would be 24 hours for

daily storage, 168 hours for weekly storage,

be used to determine the desired thickness

of insulation.

where rs is the radius of the storage and ks is

the soil’s heat conductivity. If we write the

The energy stored (Es

) can be written approximately as follows (assuming that the

specific heat does not change significantly

with temperature).

I

heat flow through the insulation as Ui(Ts-To)

per unit tank area, where T, is the temperature inside the tank:

I

I

Note that it is assumed that losses to the

surface are minimai. The system can be welI

insuIated on top, buried deeply, or placed

under the building to minimize surface

losses.

!

Alternatively, the volume required to store a

given amount of energy is:

As shown in the equation above, Shelton

found that the thermal losses to the ground

were proportionaI to the perimeter rather

than the surface area of the hemlsphere He

also showed that the earth is equIvaIent to a

ki is the thermal conductivity of the insulation being compared and R is the radius of

I

I

1

the specific heat and latent heat of phase

change per unit volume The desired thickness for the insuIation can then be given as

follows.

ty

I n

[)

the storage tank. The thermal conductiv

1] ay Shelton, ‘ U ndergroun(i Storage’ ot Ii (’at

Solar Heat I ng System\, \Ol<Ir t nt’rgk 1 7(.2), 1975,

138

4 I bld
492 Soiar Technology to Today’s Energy Needs

of different kinds of soil can vary by more

than an order of magnitude, depending on

soil composition and moisture content (see

table Xl-B-1 ). A hot storage tank under or

near a building or paved area tends to dry

out the soil surrounding it. Moderately dry

soil of a type typically found near building

sites has a conductivity of 6.0 Btu in/hr ft2

“F. (About 40 times the conductivity of polyurethane. )

If it is computed that a thickness ti of insulation with conductivity k, must be used

to reduce losses to acceptable levels without using earth insulation, burying the tank

in soil can reduce the required thickness to tl

’

where

For large storage tanks, the thermal losses

are small even if no insulation other than the

soil is used. Figure Xl-B-2 shows the annual

thermal losses from an uninsulated storage

tank (as a percentage of the storage capacity) for a hot water storage system operating

between 1200 and 2000 F. While the losses

are large for small systems, by the time the

storage capacity reaches 1 million kWh (typical of the size needed to provide 100 percent solar heating and hot water for a high

rise apartment), the annual losses have

dropped to 6 percent of the storage capacity.

Shelton also shows, however, that the

heat loss through the soil is much greater

than the equilibrium for the first few months

after the system is installed, as the soil

Table Xl-B-1 .—Thermal properties of soils

Very dry soila. ., . . . . . . . . . . . 0.1-0.2

Wet soila 

. . . . . . . . . . . . . . 0.7-2.0

Dry sandb 

. . . . . . . . . . . . . . 0.1 0.0054 19

Wetsand b ., . . . ., . . . . 1 0.042 25

Sandy clay (15% moisture)c. . 0.6 0.015 37

Concrete c. . . . . . . . . . . ., 1.6 0.046 34

Organic soila . . . . . . . . . . . . 0.8 0.021 36

Wet marshy soila . . .

Granite rock a

. . . . .

Concreted . . . . . . . . .

Dry earth, packedd 

. .

Sand d 

., . . . . . . . . . .

Moist high-conductive

Moist medium-low con

tivity soile 

. . . . . . . .

,. .,.. 0.7 0.012 54

. . . . . 0.26 0.008 31

,. .,.. 0.54 0.025 22 144

. . . . . . 0.037 95

,. .,.. 0.19 0.011 18 95

y SOil e1 , 2 0.026 46 102

duc-

. . . . . 0.4 0.013 30 100

Assorted soilsf. ... . . . . . . ., 0.3-1.3 90-110

SOURCE. Reproduced from Shelton (OP cit. ) p 143,

aR. E , Munn, Descr/pflve M/cromefeoro/ogy, 34. Academic PreSS, New York (1 ~).

bR &lger, constant values for estimation of heat economy for the agricultural meteOrO1091St Met Rurr~schau,

Heft 11 /12 (1948)

CH Lettov, Theory of surface temperature and heat transfer osctllattons near a leVel ground Surface. Trarrs Am

Geophys U 32, 189 (1951)

d Gelger , Op C(ts , PP 57~”572

‘L R Ingersoll, F T Adler, H. J. Plass and A, C. Ingersoll, Theory of earth heat exchangers for the

heat pump, Trarrs Arrr Soc lfeatlrrg !/ent//af/rrg .Errgrs 57, 167 (1951)

f Gelger , op clts , p 374
Appendix X/-B ● 4 9 3

Figure XI-B-2.-Annual Thermal Losses From Uninsulated Storage Tank

100 ‘

0.01

1 I I 1

0.03 0.10 0.30 1.0 3.0 1

Storage capacity in millions of kWh

NOTE. The thefmal lossas plo!led above are based on the resulta of ShOl~On uelw WOter an tk stof~ga medlurn IOr o wide

range of edl conductlvitles Shefton’e results were modified by OTA to aseuma ● n average storage temperature of

l@O”F, a ground temperature of 50.F, and a atorage tampemture swing of AT= SO”F.

‘Shelton, op. Clt Table XI. B.1.

5 I bld

‘1 bld

Figure XI-B-3.– Rate of Heat=Loss to Ground

Time, days

Rate of heat-loss to ground as a function of

time after initial start-up. It is assumed that

there is no heat demand, so that all the collected solar heat is available to maintain the

storage temperature at near its peak level. This

curve corresponds to a 6 ft radius ground or

gravel hemisphere storage region with a maximum temperature of 170°F with initial surrounding ground temperature of 50°F, and a solarheat collection rate of 94,000 Btu/hr for eight

hours every day (except when maximum storage

temperature would be exceeded). The ground’s

volume heat capacity is 20 Btu/ft° F and its conductivity is 0-50 Btu/hr ft20F/ft.

SOURCE:

J. Shelton (Williams College, Willlamstown MA). “Underground

Storage of Heat in Solar Heating Systems,” Solar Energy.

Volume 17, No. 2, May 1975, pages 137.143
494 ● Solar Technology to Today’s Energy Needs

Shelton’s early calculation only assessed

the thermal energy lost into the earth and

did not include an estimate of the losses

from heated earth into the atmosphere.

When ground-to-air losses were taken into

account in a detailed analog simulation of a

27,000-gallon storage pond, it was found

that total losses were approximately twice

those caculated by Shelton.’ It should be

possible to keep seasonal losses in thermal

storage ponds at acceptable levels even if

these added effects are considered, however. Clearly, this is an area where further

anaIysis is warranted

Reduction in Temperature Due to Mixing

in the Storage Vessel

It can be very difficult to compute the

temperature gradient which can be maintained in a storage vessel. The result depends strongly on the design of the system

(e.g., use of multiple interior baffles, pumping rates, tank orientation). A variety of

clever approaches are currently being examined and much more interesting work can be

expected. I n the absence of the necessary

empirical or theoretical work, it is necessary

to make some very crude approximations.

Multiple-Tank Systems

The problem of temperature degradation

due to mixing is a problem only for techniques employing sensible heat for storage

It is clear that the best way to eliminate mixing is to use separate tanks for the hot and

cold liquids. The major difficulty with this

is, of course, the added expense of another

tank.

In the case of a two-tank system of capacity Es

, each tank is as large as the one- tank

volume calculated earlier. The volume of

heat-storage liquid is the same as before,

and it is pumped back and forth between

7, ‘TaYlor Beard, F A Iachetta, L U Lllleleht, and j

W Dickey, Annual Co//ect/on and Storage of Solar

Energy for the Heat/rig of Bu//d/ngs, Report No. .?,

prepared for ERDA under contract No E-(40-I k51 36,

July 1977

the half-empty tanks as the storage is

charged and discharged Calculation of insulation thickness is similar to the earlier

case.

Even though each tank is half full, it is

stilI assumed that heat is lost through the entire wall The insulating value of the earth IS

stilI equal to a thickness kR/6 of insulation.

The additional cost of the extra tank could

be justified if the added performance permitted wouId lead to significant energy saving through increased heat-engine performance or if the cold tank can be enough colder than the lower Iimit of mixing storage that

the storage capacity of the fluid is significantly increased. The use of multiple tanks

in the same manner, but with only one tank

empty at any time, wouId resuIt in lower

costs. The analysis in this paper assumes

that multiple-tank hot water systems for

low-temperature storage are 50 percen t

more expensive than single-tank systems of

the same capacity. However, hot oil storage

has been costed on the basis of two tanks

Solid Storage Media

Another approach is to use a solid material such as stone or steel as the storage medium. As noted earlier, some thought has

been given to the possibility of using steel

ingots or other material for storing energy in

specific heat at temperatures as high as

1,0000 F. One concept would use large steel

rectangular cylinders stacked together in an

insulated container building. Heat would be

added and removed by passing steam/water

through a series of holes penetrating each

steel cylinder. The heat transfer from the hot

end of the steel cylinders and the cold ends

shouId be slow enough to permit a temperature gradient of several hundred degrees to

be maintained across the storage. This
Appendix Xl-B ● 4 9 5

would permit the withdrawal of high temperature steam at relatively constant temperature.

An ideal material for such a storage system would have the following characters:

Very low cost,

High specific heat,

Low thermal transfer from the hot to

the cold side of storage,

High thermal transfer from the charging

tubes to the storage medium, and

Ability to withstand constant thermal

cycIing without degradation

The search for an Ideal material is in a

very prellminary stage and many promising

concepts have not progressed beyond specuIation.

Reduction in Temperature Due to

Heat Exchangers

The rate of heat transfer in a counterflow

heat exchanger In which no phase change

occurs in the materIaIs and In which changes

in the specific heat are negIigible can be

written as follows:

where A is the area of the heat exchanger,

the two Iiquids at the hot side of the heat exthe cold side, and U is the overall thermal

conductivity between the fIuids, The size,

and thus the cost of the heat exchanger, will

determine the temperature difference A T

for a given rate of heat exchange. In an ideal

system design, the heat exchange area

would be chosen so that the marginal cost

of increasing the area would equal the

marginal value of extra usefuI energy resulting from a higher temperature emerging

from storage.

If one or both of the liquids passing

through the heat exchanger undergoes a

phase change, the analysls becomes significantly more complex. This situation could

occur if a phase-change materlaI is used for

storage or if water is boiled to steam whiIe

passing through the exchanger Designing

heat-exchanger systems using materials

which sol id if y can be a serious difficuIty.

If heat exchangers are used both for

charging and discharging, two separate temperature reductions would occur one during charging of the storage and one during

discharge. One of these heat exchangers can

be eliminated if the same fluid is used in the

storage and coIIector system.

Systems of the type shown in figure Xl-13

have a great advantage in that they do not

require any heat exchangers (the whole storage device being, in effect, a large heat exchanger). Liquid thermal-storage systems

can also be built without heat exchangers if

the storage medium is also the heat-transfer

fluid.
Appendix XI-C

Costs of Designs Chosen for Analysis

LOW-TEMPERATURE DESIGNS

The design chosen for hot water storage is

a tank which is buried in the ground, surrounded by a layer of polyurethane insulation (where necessary) and a vapor barrier

which protects the insulation from ground

moisture. (See figure xi-2). If the collector

uses a fluid other than water, a heat exchanger is also required. Heat exchangers

would also be required if the storage were

pressurized while the other parts of the system were not under pressure. The primary

costs are divided into three categories: the

tank itself, the excavation and backfill, and

the insulation. Costs presented here exclude

the contractor’s overhead and profit (25 percent), which is added later.

Excavation, Backfill, and Soil Compaction.

Figure Xl-5 shows as a solid line the excavation, backfill, and compaction cost per

cubic meter of tank volume as a function of

tank volume. Costs were derived from

Meansa using the following assumptions:

Excavated volume is 1.3 times the tank

volume to allow for clearance, insulation,

etc. Backfill volume is 0.3 times tank volume. Because there is a mobilization and

demobilization charge for heavy equipment, smalI jobs can be done less expensively by hand labor. For tanks greater than 3.35

m 3, excavation is done with a trackmounted, 31⁄2-cubic-yard, front-end loader.

Backfill is done by bulldozer for tanks

greater than 28 m3

, Soil compaction in all

cases is done in 12-inch layers with vibratory

plate compactors.

Hot Water or Oil Tanks

Figure Xl-5 also plots installed tank costs,

excluding excavation and insulation, for a

‘Bui/dIrJg Construction Cost Data 1976, Robert

Snow Means Company, Inc , R S Godfrey, ed , pp 18,

22, 258

496

variety of types of tanks suitable for storing

heated or chilled water or other fluids.

These prices exclude pumps and piping, It

can be seen that for the range O to 1,000 m3

it is possible to have a tank installed, including excavation and backfill, for $80/m

3

or less. The baseline design assumes $80/m3

for this size range. The assumed cost is

plotted as the dashed line in the figure.

Insulation

Insulation costs depend strongly on the

temperature of the storage and the length of

time needed for storage, The insulation

chosen for analysis is polyurethane. This

material can be foamed on in place for approximately $0,24/board foot ($101.71/m3

).9

(A thin polyethylene vapor barrier adds negligible cost.) This cost might be reduced if a

plant dedicated to producing storage equipment manufactured preinsulated tanks. The

conductivity of urethane protected by a

good vapor barrier is approximately 0.13 Btu

inch/hr ft2 oF .

Analysis

Two cases are considered: 1 ) a case which

applies to storage for use with systems

designed to supply domestic heating and

hot water (thermal energy supplied between

2000 and 1200 F and returned at 900 F); and

2) systems designed to supply absorption airconditioners and other industrial processheat loads (thermal energy supplied between 2700 and 2200 F and returned at 2000

F). Case I requires a storage volume of

0.02013 m

3

/kW ht if mixing is assumed, or

0.0146 m

3

/kW ht if there is no mixing in a

single tank. The cost of insulation in these

‘John L Renshaw of john L Renshaw, Inc (an insulating firm [n the metropolitan Washington, D C

area), private communication, August 1976.
Appendix Xl-C ● 4 9 7

cases is $101.71 Vi

, where VI is the volume

of insulation in m3

.

Case 1: C,

where E is the storage capacity in kWhth a nd

that if the above equations yield a negative

result, the earth alone provides sufficient insulation and C, = O.

The installed cost of buried tanks is

assumed to be $80Vs for tanks less than

1,000m3. For tanks with volumes greater

than 1,000m 3, an appropriate cost per cubic

meter was taken from figure Xl-22.

Case 1: Ct = $80x 0.02013E

Case I 1: Ct = $80 X 0.03221 E

(Systems larger than 1,000m3 would substitute an appropriate tank cost for $80 in the

last equation. )

HIGH-TEMPERATURE DESIGNS

Since very few of the concepts which

have been suggested for high-temperature

thermal storage have ever been fabricated

as complete systems, it is difficult to estimate what they would cost if they were produced commercially. An attempt has been

made to select for the analysis systems

which are as simple as possible, both because such systems show the greatest promise of reaching the market in the next

decade and it is much easier to estimate the

potential cost of these systems. The analysis

is fairly conservative, and may be used to

provide an upper limit for future high-temperature thermal storage costs.

in cases where the materials require factory work done off site, the bare materials

cost is multiplied by 1.6 to account for

overhead, wages, and profit in the factory.

This number is obtained from the Department of Commerce input-output tables for

“Sector 40: Heating, Plumbing, and Structural Metal Products. ”

10 Cost of onsite

assembly and installation (excluding the

contractor’s overhead and profit, which is

added later) is assumed to be 32 percent of

the cost of the components from the factory. This comes from the Department of

Commerce tables for “Sectors 11, 12: All

New Construction.’” Thus, in cases where

better estimates of assembly and installation were not available, bare materials costs

have been increased by 211 percent for materials which require additional factory

work, or 32 percent for systems which do

not.

Oil Storage for Residential Organic

Rankine Devices

The highest temperatures used in the

baseline-design organic Rankine engines for

the single family house are 4200 F (216 oC).

For storage at this temperature, a sensibleheat storage system using fuel oil has been

chosen. The oil is Iiquid at all temperatures

of interest and thus can be used as a heattransport system for conveying heat from

the coIIector to the tank as welI as serving as

the storage medium. Heat exchangers are

only needed to transfer heat to the heat

engines used to generate electricity, The

storage system operates at atmospheric

pressure. Since heat engines operating at the

small temperature differences available for

the single family system are already operating at relatively low efficiencies, the system is not able to tolerate a large drop of

temperature at the input of the heat engine,

For this reason, separate tanks are used for

hot fluids emerging from collectors and cold

liquids returned from the thermal loads to

ensure a constant high temperature to the

inlet. The assumptions and resuIting costs

are summarized in table XI-9 Costs are computed as shown in table Xl-C-1.

‘“’’ Input-Output Structure of the U S Economy

1963, ” Survey of Current Business. U S Department of

Commerce, National Economics Dlvlslon, November

1967, pp 16-47

‘ ‘ Ibid

28-842 0 - 33
498 Solar Technology to Today’s Energy Needs

Table Xl-C-1 .—Assumptions for Hot Fuel Oil

Thermal Storage, Single Family House

[420” F organic engine]

Two-tank system

No heat exchanger to collectors

Heat engine temperatures (organic Rankine) = 420° to

90” F (216° to 32oC)

aHeat exchanger temperature drop to heat engine:

10o

c (18” F)

Storage temperature swing: 439° to 108° F (226° to

42 “C)

Heat capacity of storage medium (refined fuel oil) =

0.795 kWhth/ m

3 0C

b

Thermal conductivity of insulation (foam glass): k =

0.5 Btu in/ ft2hr° F

Ground temperature = 55° F (13” C)

Credit for earth’s insulation: equivalent to insulation

thickness of (0.0833)R

aHeat exchanger constant = 4.5 kW/m20C

clns.tailed cost of insulation” (foam glass) = $1 14/m3 Of

insulation = $3.24/ft3

Installed cost of buried tanks and excavation = $160/

m

3 of oil

Installed cost of storage medium (refined fuel oil) =

$146/m

3

a

lnstalled cost of heat exchanger to heat engine = $80/

m

2 of heat exchanger

Tanks, excavation, oil = 2.092E$

Heat exchangers = 1.78P$

NOTE Costs exclude contractor’s overhead and profit (ZSo/O), which

IS added later. “E’” IS storage capacity in kWhth. “d” Is

storage Interval In hours. “R” IS storage tank radius “P” IS

discharge rate In kwth

aR w Hall~t and R L Gervals, Cert(ra/ Rece~ver Solar Thermal power

System, Phase 1, F(na/ Report, MDC G6040, McDonnell. Douglas

Astronautics Company, January 1976

%ee figure Xl-B-1

cMeans Bu//d/ng Cons frucf/on COSf Data, 1976, P. 111

Therminol-55/Rock Storage

The TherminoI-55/rock-storage system is

similar to the hot fuel oil system just examined. Two tanks are used to maintain a high

discharge temperature and thus a high “temperature efficiency” (for heat engines). The

rocks are assumed to occupy 70 percent of

the storage volume. The assumptions and resulting costs are summarized in table XI-C-2.

Storage in Steel Ingots

The steel-ingot system can eliminate the

need for heat exchangers, but this requires

the use of 150 psia steam in the collector

Table Xl-C-2.—Assumptions for Therminol-55/

Rock Thermal Storage [600 “F heat engine]

Two-tank system: no heat exchanger to collectors;

70% rocks by Volume

Heat engine temperatures: 600° to 100” F (316° to 38° C)

aHeat exchanger temperature drop to heat engine:

10” C (18° F)

Storage temperature swing: 618° to 118°F (326° to 48oC)

Heat capacity of Therminol-55: 31 Btu/ft3° F (0.577

kWh/m3° C)

Heat capacity of rocks: 27.3 Btu/ft3° F (0.509 kWh/m3° C)

System heat capacity: 28.4 Btu/ft3° F (0.529 kWh/m3

“c )

b

Thermal conductivity of insulation (foam glass): k =

0.6 Btu in/hr ft2

° F

aHeat exchanger constant = 4.5 kW/m2

° C

Ground temperature: 55° F (13° C)

Credit for earth insulation: equivalent to insulation

thickness of (0.1)R

c

lnstalled cost of insulation (foam glass) =

$114/ m

3 of insulation = $3.24/ft3

a

lnstalled cost of heat exchangers to heat engine =

$80/m2 of heat exch.

Installed cost of rocks = $0.01/lb x 140 lb/ft3 x 70% =

$0.98/ft3 storage = $34.61/m3

Installed cost of Therminol-55 = ($.38matl + $.05

shipping)/lb x 43 lb/ft3 x 30% = $5.55/ft3 =

$195.89/m 3 storage

Installed cost of buried tanks and excavation = $160/

m3 of storage:

Tanks, excavation, Therminol, rock = 2,655E$

Heat exchangers = 1.78P$

NOTE: Costs exclude contractor’s overhead and profit (250/.), which

IS added later. “E” IS storage capacity in kWh “8” is .sforage interval In hours “R” is storage tank ra~us. “P” IS discharge rate In kWth

aHa[let and Gervals, MDC G6040.

b%e figure Xl- B-1

cMeans, 1976, Q . 111

system. This is assumed to be acceptable

since the heat engine will operate at this

pressure, and thus an operator familiar with

the engine should be able to supervise the

steam transport system. The ingots could be

integrated into the structure of the building

or buried in the earth. Earth burial is assumed for the following calculations, although individual installations may present

other opportunities. Excavation and backfill

costs are taken from figure XI-5. The Jet Propulsion Laboratory (JPL) has calculated that
Appendix XI-C ● 4 9 9

a system operating between 9500 and 1000 F

(510 0 and 38 “C) can be discharged by about

68 percent of its total sensible-thermal capacity before the output steam starts to fall

below 950 ° F .

12 The analysis therefore

reduces the thermal capacity of the steel accordingly and assumes that al I of the discharge steam is at 9500 F. The following cost

assumptions were also taken from the JPL

study: steel ingots at $.15/lb; welded headers

at $50/hole ($25 each end); rail transportation of materials at $.01/lb; miscellaneous

(flow valves, controls, sensors, weatherproofing, etc. ) at $.0067/lb of ingots. It also

is assumed that the ingots are piled in a

stack whose shape is close enough to a cylinder (with length = 4R) that the insulation

calculations can be done using equations

already developed for cylindrical tanks. The

assumptions used are shown in table Xl-C-2.

High-Temperature Phase Change Storage

Several designs for storing thermal energy

in the heat of fusion of sodium hydroxide

have been examined, and operating units of

at least two different approaches have been

constructed. 3 These units use electricity to

charge the storage to about 9000 F. Total

system cost for these devices is estimated

to be between $1 .35/MBtu and $1.50/MBtu

($4.61-512/kWh th). Examining figure XI-19, it

can be seen that the available energy for use

at 9000 F is approximately twice the available energy for the temperature swing between 6200 and 4200 F which is required for

the heat engine. The price appropriate for

the on site application wouId thus be approximately $3/MBtu ($10.24/kWht) JPL has

designed a sodium hydroxide storage system

“R H Turner () PL), “Thermal Energy Storage Using

Large Hollow SteeJ Ingots, ” Sharing the Sun: So/ar

Techrto/ogy in the Seventies. J olnt Conference, American Section, International Solar Energy Society and

Solar Energy Society of Canada, Inc , Wlnnlpeg, Canada, Aug 15-20, 1976, Vol 8, pp 155-162

‘ ‘R E Rice, Therma/ Storage for Application to

Energy Conservation, Comstock and Wescott, Inc ,

April 1975, Cited In Bramlette, et al , (Sandla Laboratories, Llvermore) SAN D75-8063

for use with a solar system which operates

between 6500 and 4000 F for a cost of approximately $3.7/MBtu ($12.63/kWhJ.

The system which will operate with the

Stirling cycle will have a very similar design.

The costs of the two systems are estimated

in paralIel in the following discussion.

The heat of fusion storage system is assumed to be produced in factory-assembled

modules. Each modular tank contains within

it a bundle of sealed, long, narrow, cylinders

full of the storage material. The cylinders

occupy three-fourths of the tank volume,

and heat-pipe fluid circulates in the space

around the cylinders, as shown in figure

IV-20. During charging, the heat-pipe fluid is

heated directly in the solar collector, and

during discharging, the heat-pipe fluid condenses at the heat engine, eliminating the

expense of separate heat exchangers. Each

cylinder is assumed to be 4 feet long and 3

inches in diameter. There are 60 cylinders

per tank, and the tanks are 59 inches long

and 27 inches in diameter. The cylinder

walls are 0.040 inches thick. This is thick

enough to contain the weight of the storage

material if adequate room is provided for

expansion during phase changes. The volume of containment material per cylinder is

thus 302 cm3

, and each cylinder can contain

5,260 cm3 of storage material. The characteristics of potential container materials are

shown in table Xl-C-3.

The cylinders are assumed to be made of

stainless steel. Although stainless steel is not

completely resistant to corrosion by pure

fluorides, N. V. Philips reports that by adding a small amount of aluminum to the melt,

all corrosion is eliminated. Corrosion testing was done for more than 14,000 hours at

850 “C with ordinary 18/8 stainless steel. 5

Each tank is a double-wall pressure vessel,

insulated by a vacuum and multifoil super14) Schroder (N V Phliips Aachen Lab ), “Thermal

Energy Storage and Control, ” journa/ ot Engineering

for /ndustry, August 1975, pp 893-896

“j Schroder (N V Philips Aachen Lab ), private

communlcatlon, jan 13, 1977
500 . Solar Technology to Today’s Energy Needs

Table Xl-C-3.—Assumptions for Steel-Ingot

Thermal Energy Storage

Steam Rankine engine: no heat exchangers

Heat engine temperatures: 950° to 10O”F (510° to 38oC)

Storage temperature swing: 950° to 100” F (510° to 38°C)

Storage temperature swing: 950” F to 100” F (510oC to

38” C)

Storage medium: cast steel ingots, 60 ft long, 1 ft wide,

1 ft high; 9 axial holes, 2 in diameter per ingot

Headers: 2 in diameter, low-alloy, seamless pipe

Schedule 50, formed into thermal stress expansion

loop and welded to ingot holes

Steel heat capacity = 58 Btu/ft3° F

System heat capacity (20% holes; 32% unrecoverable)

= 0.608 kWhth/m3° C

aSee figure Xl- B-1

bMeans, 1976, p 111.

NOTE Costs exclude contractor’s overhead and profit (2s0/. ), which

IS added later. “E” IS storage capacity In kW h

storage Interval In hours. “R” IS radius of the p~~e ‘;~I’; ;;

possible to use concrete or some other Inexpensive material

instead of steel, the cost could be reduced by a factor of three

or more

insulation. This type of insulation has a thermal conductivity of 0.0049 Btu in/hr ft 2 oF. 16

The cost of the metallic foil insulation is

estimated at $2.00/ft 2 of surface area, and

the resultant thermal conductivity is so low

that even seasonal storage results in “very

small heat losses.’” 7 The tank walls are as-

“N. E. Polster and W R. Martini (University of

Washington), Self-Starting, Intrinsically Control/cd

Stirling Engine, 11th I EC EC.

“R L, Pens and R. J. Fox (Aeronautronic Ford Corp.

and Walt Disney Productions), A So/ar/Stir/ing Tota/

Energy System, unpublished, 1976.

sumed to be 1⁄4-inch stainless steel, fabricated at $2.00/lb. 8 The two heat pipes are

assumed to add $200 each to the cost of

each tank. 9

The installed cost of the cylinders is estimated using the materials costs in tables

Xl-4 and Xl-C-4, adding $().1()/kg for shipping,

and multiplying by the factor of 2.11 to account for factory and onsite fabrication and

instalIation. The cost assumptions are summarized in tables Xl-C-5 through Xl-C-7.

BATTERY STORAGE COSTS

The costs of battery storage used in the

analysis conducted in this study are summarized in figure Xl-28 and table XI-11 .

There appears to be a reasonable concensus

that costs as low as $55/kWh are feasible in

the “intermediate term, ” but a considerable

amount of disagreement about how far

prices will fall in the long term. The Bechtel

summary of battery costs estimated that advanced batteries could be produced for $10

to $25/kWh20 while other sources have estimated that prices below !$25/kWh are unlikely .21 22 The “long-term” cost $11/kWh

shown in the table reflects an assumption

that a low-cost iron-REDOX system has been

developed.

Neither estimate of O&M cost given in

table Xl-8 would add appreciably to the

overall costs of battery storage. Even if

O&M costs for advanced batteries are a factor of 2 higher, the O&M costs would still be

minor. Consequently, 0.0284/kWh has been

used for all three cases in table Xl-11.

‘

a Ibid,

“Ibid

~OAn Engineering Study of a 20 M W, .200 MWh f-=dAcid Battery Energy Storage Demonstration P/ant,

Bechtel Corporation, ANL Contract No. 31-109-

38-2692, October 1975.

*’James Birk (E PRI), private communication, Jan.

20,1977.

ZZAn Assess~enr of Energy Storage S ysterns suitable

for Use by Electric Utilities, Fina/ Report by PSEG on

ERDA Contract No. E (11-1 }2501, Vol. 11, July 1976,

pp. 4-60.
Appendix XI-C . 501

Table Xl-C-4.—Containment Materials

Density

3

Yield strength ● cost

Material (kg/m ) (N/m2) ($/kg)

8515-70 carbon steel. . . . 7.8 X 103

3.1 x 108.22

304 stainless steelab . . . 7.9 x 103 2.4 X 108 1.76

Steelite-21 abcde. .

. . . . . 8.3 X 103 5.7 x 108 40.00

Inconel ce. . . . . . . . . . . . . 7.8 X 103 2.7 X 108 11.00

Hastelloy s

abcde. 

. . . . . . 9.0 x 103 3.8 X 108 26.00

‘ Room temperature values

aOxldatton resistant

bHlgh.temperature al IOY

CReSIStant to chemical attack

dReslstant to most fluorldes

eReslstant to fluorldes If Al IS added to the fluorlde

SOURCES T T Bramlette (Sandla Laboratories, Livermore), compiled for OTA, 1976.

Note e added by J Schroder (N. V. Philtps Aachen Lab ), Dnvate communl -

cation, Jan 13, 1977

The salvage value (or reduced replacement cost) for near-term batteries is principally the value of the lead in the battery.

The replacement price for intermediateterm batteries is based on a crude average

of the fractional replacement prices projected in table Xl-8. Most of the advanced

batteries use inexpensive materials which

wouId have negligible salvage value. Consequently, no salvage value is assumed. If one

of the batteries containing Iithium were

used, the replacement price would clearly

be less than the inital price, since lithium

can be effectively recycled.

Battery storage systems for utility applications are expected to use a large number of cells which have individual storage

capacities of 5 to 40 kWh. 23 These are the

systems for which virtualIy alI of the available cost projections apply. It is expected

that smaller systems will require somewhat

smaller cells to obtain reasonable system

voltages Detailed studies of the relative

cost of such systems have not been completed. However, the direct product cost

($/kWh) for a 7 kWh mass-produced cell

would probably be about 14 percent higher

J ‘james R [31rk, The Lead-A c/d Battery for E/ectr/c

Uti//t/e~ A ReL Iew and Ana/ysIs, presented at the ERDA EPRI Lead-Acid Battery Workshop 11, Dec 9,1976

than a 50 kWh cell, and batteries in the 20

kWh size range may cost 20 to 25 percent

more than batteries for large storage facilities. Detailed design studies now underway

may change this estimate. 24

Table Xl-C-5 .—Latent-Heat Storage Tank

Assumptions

Volume of stainless steel in tank wall = 0.04477m3

Surface area of tank = 38.48ft2

Tank wall cost = (0.0447 m3)(7,900kg/m3)( 2.2lb/kg) ($2/lb)

= $1,560

Insulation cost = (38.48ft2)($2.00/ft2) = $77

Heat pipe cost = $400

60 cylinders per tank

Cylinder cost = (302cm3)(.0079kg/cm3)($1.86/kg)

(2.1 1) = $9.36/cylinder

NaOH cost + (0.00526 m3)(1,784kg/m3)($0.65/kg)

(2.11 = $12.87/cylinder

NaF/MgF2 at $0.50/lb = (0.00526m3)(2190kg/m3)

($1.20/kg)(2.11) = $29.17/ cylinder

NaF/MgF2 at $0.25/lb = (0.00526m3)(2190kg/m3)

($0.65/kg)(2.11) = $15.80/ cylinder

Volume of storage material per tank = 0.3156m3

Overall volume of tank = 0.60m3

Total installed tank, NaOH: $3,371 plus excavation and

backfill

Total installed tank, $0.50 NaF/Mg F2: $4,349 plus excavation and backfill

Total installed tank, $0.25 NaF/Mg F2: $3,547 plus excavation and backfill

24Nlck Maska lick (Westinghouse Corporation), private communication, Jan. 31, 1977
502 ● Solar Technology to Today’s Energy Needs

Table Xl-C-6.—Assumptions for NaOH

Latent-Heat Storage [600° F heat engine]

NOTE Costs exclude contractor’s overhead and profit (250/.), which

IS added later. ‘(E” IS storage capacity In kWht IflSulatlOn

IS adequate for seasonal storage

aHallet and Gervals, MDC G6@$0

bsee table XI- 7

CR L. Pens and R J FO X.

For purposes of this study, we increase the

large system prices by 10 percent for the

commercial and multifamily residential systems, and 20 percent for home systems.

POWER-CONDITIONING COSTS

As noted earlier, the bulk of the cost of

power-conditioning apparatus results from

the cost of the inverter system. Estimates of

the cost of voltage regulators vary from 1 to

Table Xl-C-7.–Assumptions for NaF/MgF2

Latent-Heat Storage [1 ,400°F heat engine]

cost :

(.50 NaF/mg

F2 $/kg)

Total storage

cost :

(.25NaF/

F2 $/kg)

aHallet and Gervals, NDC G6040

bSee table Xl-7

6 percent of the cost of the inverter. The

cost of the interface varies from about 10 to

20 percent of the inverter cost for systems in

the kilowatt range to about 2 percent of inverter cost for systems in the megawatt

range. Estimates of current and potential

power-conditioning costs are shown i n

figure XI-28.

The prices chosen to represent “nearterm, ” “intermediate,” and “speculative”

technologies are chosen somewhat arbitrarily to represent the spectrum of estimates

shown. The “near-term” prices selected are

somewhat lower than the average prices of

contemporary power-conditioner devices

since many of the units now available are
Appendix Xl-C .503

overdesigned for solar application, and

many of the small systems shown operate at

voltages much lower than would be required

for solar applications (low-voltage systems

are usually more expensive than higher voltage devices with similar power capabilities).

In the intermediate term, it can be

assumed that at the lower power levels, increased production volume will lower

prices, although in many of today’s systems,

standard components such as inductors and

capacitors represent a significant fraction of

the cost, and this will limit the production

economies possible. At higher power levels,

systems wilI probably continue to be essentially custom-designed, but increased engineering experience shouId lower costs somewhat, as assumed for the intermediate case

of figure Xl-28.

in the longer term, it can be assumed that

power-conditioner units in the smaller sizes

can be made for substantialIy lower prices

by mass-producing units designed with

power transistors so that the use of components such as inductors is minimized.

Westinghouse has estimated that such units

could be produced for $50 to $70/kW. 25 A t

intermediate and higher power levels, market size and component size will probably

prevent automated production, and the

price may go up for some sizes as suggested

by the curve sketched for the “long-term”

case i n figure Xl-28

It should be noted that the prices dis -

cussed so far have been in terms of rated

capacities which are related to the normal

load of the system. Most systems can actually supply 1.5 to 3 times the rated capacity,

depending on the specific characteristics of

J 5P F Plttmdn, Progrdrn A4andger for Westinghouse

F let trlc Corporat Ion Re$earch I aboratorie>, F/rra/

Report on Conceprud/ Lies/gn and S y$tems An~/\\l\ of

Photovo/talc Power $ ysterns, ERDA Contrdct N o

I (1 1-.2744), December 1976

the power conditioner and the load. 26’ I n the

integrated system cost runs, it has been

assumed that power conditioners have a

peak capacity 1.5 times their rated capacity.

BUILDING AND OTHER COSTS

I n addition to the battery and power conditioner costs, there is a significant cost

associated with instalIation, electrical wiring, and instrumentation, and the room in

which the battery system will be housed. No

detailed estimates of these costs were available for systems of the size considered in

this study, It was assumed that the batteries

would be located in the basement of homes

or in the equipment rooms of apartments

and shopping centers. Unfinished basement

space in such buildings costs about $5.00 to

$7.50 per square foot. “Building and Other

Costs” were assumed to be twice the cost of

the space and it was assumed that the batteries we arranged so there were 2 to 3 kWh

per square foot of floor space for present

lead-acid battery systems. It is assumed that

“advanced battery systems” wiII have higher

energy densities, and require less space.

REDOX batteries do not have a high energy

density but it should be easier to integrate

the liquid storage tanks which make the

system bulky into building space than it

wouId be to find space for more complex

systems requiring high temperatures or

potentially hazardous materials It was

therefore assumed that the building and

other costs associated with the REDOX

systems would be no greater than those of

other batteries. It was assumed that the

“building and other costs” and power conditioner costs scale with battery capacity in

the same way (see table Xl 1-11 )
Chapter Xll

HEATING AND COOLING EQUIPMENT
Chapter Xll.— HEATING AND COOLING EQUIPMENT

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507

Electric Air-Conditioners and Heat Pumps.... 507

System Performance. . ..................510

Potential for Improving Performance .. ..511

Direct Fossil-Fired Heating and Air-Conditioning Equipment . . . . . . . . . . . . . . . . . . . . 514

Heating Equipment. . . . . . . . . . . . . . . . . . . . . 514

Potential for Improving Performance .. ..517

Absorption Air-Conditioning ... ............519

System Performance. . ..................520

Conventional Gas and Electric Water Heaters. 522

Operating Costs. . . . . . . . . . . . . . . . . . . . . . . . . .522

Adaptation of Conventional Equipment to

Solar Power . . . . . . . . . . . . . . . . . . . . . . . ..523

Solar Heat Engines. . ...................524

Solar Absorption Equipment . . . . . . . ......524

The Adsorption Cycle System . .........524

LIST OF TABLES

Table No. Page

l. Cooling Coefficients of Performance for

Systems Smaller Than 65,000 Btu/Hour. ...5lO

2. California Standards for Cooling Equipment 511

3. Average Cost of Maintenance Contracts for

Residential Heating and Cooling Equipment 522

Table No. Page

4. Cost of Maintaining Commercial Heating

and Cooling Equipment . ................523

LIST OF FIGURES

Figure No. Page

l. A Typical ’’Split System” Heat-Pump

Installation. . . . . ......................508

2. A Typical Packaged Outdoor Chiiler .. ....509

3. 1976 Air-Conditioning Performance of

4.

5.

6.

7.

8.

9.

10.

Units Smaller Than 65,000 Btu/Hour .. ....510

Performance of the Carrier Split-System

Heat Pump . . . . . . . ....................512

The Seasonal Performance of Heat-Pump

Units as a Function of Local Climate .. ...513

Estimated Cost of lncreasing the

Performance of Air-Conditioners From

the lndustry Average COP of 2.0 to the

Performance Levels Indicated . ..........513

Some Examples of Proposed Advanced

Heat-Pump Cycles. . ...................515

Residential Heating Systems. . ..........516

Efficiency of Gas Furnaces . ............516

A Fossil-Fired Heat-Pump System . ......517

11. Basic Single-Effect Absorption Refrigeration Cycle . ........................519

12. Estimated Refrigeration Unit Cost Per Ton 520

13. Coefficient of Performance Versus

Supply Water Temperature. . ............521

14. An Adsorption Chiller. . ................525
Chapter XII

Heating and Cooling Equipment

INTRODUCTION

This chapter has two major objectives: to estimate the cost of providing

space conditioning from conventional electric equipment as well as from oiland gas-fired devices, and to analyze the performance of systems which can

be coupled with solar devices. Technologies examined include electric and

absorption air-conditioners, heat pumps, and conventional gas- and oil-fired

boilers. Systems examined are compatible with loads varying from that of a

single family residence to the requirements of a district heating system.

Much of the data needed to perform a careful study of the cost of providing

heating and cooling from conventional equipment is not easily available.

Some of the relevant data remains proprietary and, in a number of cases, adequate measurements of performance in realistic operating environments

have never been taken. A detailed study of the performance of many heating

and cooling devices is now underway at the Building Environment Division of

the National Bureau of Standards. A more accurate comparison of systems

wilI be possible when that study is completed.

Given the uneven quality of the information utilized, no attempt should be

made to use the results to judge the relative merits of different conventional

approaches to space-conditioning. The object of the cost computations is

simply to provide a reasonable background against which to test the

economic merits of solar equipment. These computations are based on the

most reliable information now avaiIable to OTA, but the lack of precision is

f reel y acknowledged.

ELECTRIC AIR-CONDITIONERS AND HEAT PUMPS

A typical residential air-conditioner/heatpump installation is iIlustrated in figure

Xl 1-1, and a large central chiller is shown in

figure Xl 1-2. Both units employ the same

basic refrigeration cycle, although the

smaller units usually cool and dehumidify

room air directly while the larger systems

typically produce chilled water which is

piped to fan-coil units in various parts of the

building. The cooling systems have three

basic components: 1 ) a unit which permits a

refrigerant to expand, vaporize, and absorb

heat from the room air (or water system); 2) a

compressor which compresses the heated

vapor (increasing its temperature); and 3) a

condenser located outside the building

which rejects the heat absorbed from the

room air into the atmosphere (condensing

the compressed vapor to a Iiquid). I n

‘‘s i ng I e-pa c k age’ units, alI three functions

are provided i n the same unit and can b e

connected directly to the ductwork (or

chilled water system) of the building. I n

“split-system ” devices, refrigerant is sent to

an air-handIing unit inside the building. (This

system is illustrated in figure Xl l-l. ) Another

distinction which is frequently made i n -

volves the technique used to compress the

refrigerant vapor. Smaller units typically use

a simple piston system for compression and

are called “reciprocating” units. Larger u nits

may use centrifugal pumps or screw compressors for this purpose.

Heat pumps use the same three basic

components as the air-conditioners described above, but the cycle is reversed. I n

the heating cycle, the indoor air absorbs

heat from the refrigerant and heat is acquired by the refrigerant from the outdoor

507
508 Solar Technology to Today’s Energy Needs

Figure XI I-I .—A Typical “Split System” Heat-Pump Installation

SOURCE. Carrier CorDoratlon

fan unit (the “condenser” in the cooling

model).

Heat pumps which can extract useful

energy from outdoor air temperatures as

low as 00 F are now on the market, although

system performance is seriously degraded at

low temperatures. The electricity used by

the system can be considerably reduced if a

source of heat with a temperature higher

than that of the outside air can be found.

Lakes or ground water, for example, are

usualIy above ambient air temperatures during the winter and can be used to provide a

source of input heat if they are available.

Many buildings have sources of heat (such

as Iighting, mechanical equipment, rooms

with large southern exposures, etc. ) which

can be recovered and used to heat a storage

reservoir. A number of small heat pumps

can be located throughout a building. Some

of these pump heat from warm areas into

the water reservoir, while others recover

this energy and pump it into rooms requiring

heating. Solar energy can also be used to

provide a source of heated water. Systems

which extract heat from water are called

“water-te-air” heat-pump systems, while

units extracting energy from the air are

called “air-to-air” systems.

While less than half of the residential

units in the United States were equipped

with air-conditioners in 1974, the demand

for air-conditioners is growing. 1 in 1974,

about 45 percent of all single family home s

and 34 percent of all multifamily dwelling

units were equipped with some type of airconditioner. 2 A DOE forecast estimated that

IGordian Associates, Inc , Evacuation of the A;r-tG

Air Heat Pump for Residential Space Conditioning,

prepared for the Federal Energy Administration, Apr

23,1976, p. 114

‘Ibid , p 115
Ch. XII Heating and Cooling Equipment 509

ROOM

THERMOSTAT IN

CONDITIONED

SPACE

Figure Xll-2.– A Typical Packaged Outdoor Chiller

,,

SOURCE Carrier Packaged Outdoor Air-Cooled Llquld Chillers Carrier Corporation

by 1985, air-conditioning will be installed in

75 percent of all residential and commercial

buildings and will require about as much energy as electric heating. 3

Heat pumps are likely to have a far

smalIer impact on overall U.S. energy consumption unless some dramatic change occurs in public acceptance of the units. Less

than 1 percent of U.S. homes currently have

heat pumps, and only about 7 to 8 percent

of the new housing starts in 197.5 used the

‘Nationa/ P/an for Energy Research Development

and Demonstration, Vo/ume /, ERDA-48, p B 10

a *

ST - STARTER

FD - FUSEO DISCONNECT

1974, Form 30GA-5P

system. 4 The growth of the market has been

slowed by the sensitivity of buyers and

builders to the initial cost of the equipment

(which is higher than conventional electricresistance heat), and by the fact that

regulated gas prices and promotional electric prices have made the cost of operating

competitive heating systems artificially IO W

Concerns about reliability have also been a

problem. Some of the heat pumps marketed

in the early 1960’s were extremely unreliable, and sales of the units fell steadily be-

‘Gordlan Associates Inc , op clt , p v
510 ● Solar Technology to Today’s Energy Needs

tween 1965 and 1970. While most of the reliability problems have been resolved, a recent study showed that the problem has not

vanished. The compressors examined in the

study failed at a rate which varied from 3.6

percent to an astonishing 23.3 percent per

years A 5-percent annual failure rate is considered tolerable for this kind of spaceconditioning equipment, and apparently

very few manufacturers were able to meet

this standard.

In spite of their relatively small share of

the U.S. space-conditioning market, heat

pumps are likely to be in direct competition

with solar equipment during the next few

decades. They would tend to appeal to the

same category of buyers, those willing to

consider Iife-cycle costing, and are Iikely to

offer the lowest Iife-cycle cost of any nonsolar space-conditioning system if the price

of heating oil and natural gas increases

significantly.

SYSTEM PERFORMANCE

The performance of heat pumps and airconditioners now on the market varies greatly. Figure Xl I-3 indicates the performance of

air-conditioners smaIIer than 51⁄2 tons now

on the market. The difference in performance reflects both the quality of design and

the cost of the unit. High-performance units

may also result from a fortuitous combination of components. Manufacturers cannot

afford to design condensers optimalIy suited

for all compressors to which they may be attached, and some combinations of these

units (in the absence of information of comparable quality about the variety of systems

examined here) may therefore result in a

high-efficiency system. As a result, while

there are a few units on the market with very

high efficiencies (figure XII-3, for example,

indicated that 10 percent of the units on the

market have a coefficient of performance

(COP) greater than 2.5), this performance is

not avaiIable in alI size ranges.

51 bld

Figure Xll-3.— 1976 Air-Conditioning Performance

of Units Smaller Than 65,000 Btu/Hour

.“

1 00%

1976 Industry Average 2.00

50% -

I I I I I

1.5 2.0 2.5

Tables Xl l-l and Xl I-2 give some indication of the performance which can be expected from different cooling devices, T h e

1976 industry average COP was 2.00.

Heat pumps were about 5 percent less efficient than the average air-conditioner,

There are a variety of reasons for this. Heat

pumps cannot be optimized for maximum

cooling performance as somewhat more

complexity is required in the coolant piping,

and the valve which switches the direction

of the refrigerant when the system is

changed from heating to cooling introduces

some inefficiencies.

Under some circumstances, small window

units are capable of better performance

than central air-conditioners; central units

Table XII-1 .—Cooling Coefficients of

Performance for Systems Smaller Than

65,000 Btu/Hour (1976 industry averages)

Average COP

All ARI listings 2.00

Split-system cooling 2.00

Single-package cooling 1.90

Single-package heat pumps 1.94

Split-system heat pumps 1.90 — ——— .—

SOURCE George D Hudelson (Vice PresldentEnglneerlng, Carrier

Corporation), testimony before the Caltfornla State Energy

Resources Conservation and Development Commlsslon, Aug

10, 1976 (Docket No 75, CON3)
Ch. XlI Heating and Cooling Equipment ● 511

Central Air-Conditioners

Heat pumps (cooling mode)

Air-conditioners

Room Air-Conditioners

All systems with capacity greater

than 20,000 Btu’s

Other heat pumps

Other air-conditioners

All systems using voltages

greater than 200 v.

Other heat-pump systems

Other air-conditioners

1.96 2.2

2.05 2.34

2.05 —

2.08 —

2.20 —

— 2.40

— 2.43

— 2.55

.—

“No system m~y be sold n fhe State atter this date with a COP below the standard

must pump chilled air or refrigerant over

significant distances, and require more

energy to operate the pumps and fans needed to transport chilled air or liquids to and

from the space to be cooled. The performance of large, central chilling units themselves (such as the one shown in figure Xl 1-2)

is better than window units, however. The

larger units typically employ more efficient

motors and more sophisticated designs;

many units are able to achieve better performance at part loads by adjusting the flow

of refrigerant (Many of these improvements

couId, of course, be incorporated in a

smaller unit at some increase in the initial

cost. ) The advantages of larger systems are

offset, however, by losses incurred in other

parts of of the system.

A large number of designs are employed,

and overall performance varies greatly from

one installation to another. Some systems

may require significant amounts of pumping

energy to either move chIIled Iiquids or air

to different parts of a buiIdIng or to operate

a cooling tower which may be located on

the roof

The performance of electric-cooling and

heat-pump systems also varies as a function

of the temperature and humidity of both the

inside and outside air. This is due both to the

fact that the theoretical capacity of a unit

varies as a function of these parameters, and

because most units must either be fully on

or fully off. The load control achieved by

“cycling” the system from full capacity to

zero output requires heating or cooling

large parts of the system before useful space

conditioning can be performed. Using

energy to heat or cool the units decreases

the system’s efficiency. The dependence of

a typical residential heat-pump unit COP on

the outdoor temperature is shown in figure

Xl 1-4. The fact that the heat pump’s capacity

to produce heat decreases as the outside

temperature decreases results in a highly

temperature-dependent heating mode, A

system large enough to provide 100 percent

of the heating load at the lowest anticipated

temperature would be prohibitively expensive in most locations, and a most common

compromise is to assist the heat pump with

electric-resistance heat whenever its capacity falls below the heating demand. The

average COP of a heat-pump system during

the winter season is called the seasonal

performance factor (SPF). This parameter is

shown in figure Xl I-5 as a function of local

climate. As expected, the average COP of

heat pumps is lower in northern parts of the

count ry.

The performance of water-to-air heatpump systems can be significantly higher

than air-to-air systems if heated water i s

available. When 600 F water is available,

most commercial units have COPS in the

range of 2.5 to 3.5,6 but units with COPS as

low as 2.0 and as high as 3.7 are on the

market.

Potential for Improving Performance

Research which could significantly improve the performance of these devices i s

currently underway in the laboratories of a

number of heat-pump and air-conditioner

manufacturers. Figure Xl I-6 summarizes a re-

‘)LIIreC ~or} of Cert/f/ed UnJtJry A )r-( ond~t)oners,

Unitar} He<?t Pumps, Sound-Rdtcd ~~ljtdoor un~tar]’

Lqu Iprncn(, Cerrtra / $} stem }fLIm Idit Iers, AI r-Condlt IcjrI I ng d n~ Refrlgerat Ion [ nst It u t(>, 1‘j76
512 ● Solar Technology to Today’s Energy Needs

Figure Xll-4.– Performance of the Carrier Split-System Heat Pump

I I I I I 1 I I 1 I 1 I I

I o 10 20 30 40 50 60 70 80 90 100 110 120

Ambient Temperature

Model 38CQ020 ARI ratings:

Assumptions used in computing

system performance:

Heating mode nominal capacity

21,000 Btu/hour. COP at high temperature is 2.9, COP at low temperature is 1.7.

Cooling mode nominal capacity is

19,000 Btu/hour. COP is 2.1.

Heating mode entering indoor air

is 70- F (db) heating demand includes energy used for defrost

balance point at 30’ F.

Cooling mode entering indoor air

is 80 F (db) and 67 F (wb). Fan

power is 0.2 kW.

Energy use includes: compressor motor demands; resistance heat;

the demands of indoor and outdoor fans; and the energy used in

defrost cycles. The air-flow was assumed to be 700 cfm. Assumptions

made about decrease in efficiency due to part load conditions were

not explained in the literature.

SOURCE Carrier Spilt-System Heat Pump Outdoor SectIons Carrier Corporation 1976, Form 38CQ-l P
Ch. XII Heating and Cooling Equipment 513

Figure XII-5.– The Seasonal Performance of Heat-Pump Units

SOURCE What IS a S/rig/e Packaged l-leaf Pump and How Can It Save You Money?, Carrier Corporation, Catalog No 650.069

Figure Xll-6.— Estimated Cost of Increasing the Performance of Air-Conditioners

From the Industry Average COP of 2.0 to the Performance Levels Indicated

(estimates assume production rates equivalent to current production rates)

2-piece cooling

/

20 21 22 23 24 25 26

System Coefflclent of Performance

SOURCE George D Hud~lson (Vice Prewdent - Englneerlng Carrier Corp } Presenlatlon to the solar Emmy Resources Conservation and Develop

ment Commlsslon of Call forma Aug 10 1976 Docket No 75 CON 3
514 ● Solar Technology to Today’s Energy Needs

cent series of estimates of the increase in

air-conditioning COP achievable without

changing the basic design of the air-conditioning system and using a compressor unit

which is currently available, and the cost of

producing these new designs. Equipment incorporating these new designs could be

made in the next few years. The requirements which will be imposed on airconditioners and heat pumps sold in the

State of California during the next 5 years

are shown in table Xl 1-2.

Looking further into the future, a number

of systems have been proposed which could

increase the COP of air-conditioning

systems and heat pumps by as much as so

percent. A series of designs being considered by the General EIectric Corporation

is indicated in figure Xl 1-7. Researchers at

G.E. believe that it would be possible to

achieve an approximate 50-percent increase

in the average COP of both heating and

cooling for an increase in the initial cost of

the unit of about 20 to 30 percent 7 It should

be noted that performance can be improved

by increasing low-temperature performance,

high-temperature performance, or both, The

speed with which these new units appear on

the market will depend strongly on the company’s perception of whether the public is

willing to invest in equipment which can

reduce their annual operating expenses over

the long term. These attitudes, of course,

may be infIuenced by legislative initiatives.

DIRECT FOSSIL-FIRED HEATING AND

AIR-CONDITIONING EQUIPMENT

HEATING EQUIPMENT

The majority of residential and commercial buildings in the United States are

heated with direct-fired oil and gas furnaces

and boiIers. There is considerable controversy about the typical operating efficiencies

of these systems. One reason is that remarkably Iittle is known about the performance

capabilities of these systems in actual operating environments, and the literature in the

area is filled with inconsistent information.

Some indication of the difficulty can be

seen by examining figure Xl 1-8, which indicates the performance estimates made by

a variety of different organizations. Performance undoubtedly varies with the age

of the unit, its installation, its position in the

building, and a variety of other variables

which are difficult to hold constant.

Another reason for the controversy is the

inconsistency in the definition of efficiency.

Until recently, the most common value

quoted was the steady-state or full-load

combustion efficiency, which is defined as

the ratio of useful heat delivered to the furnace bonnet divided by the heating value of

the fuel.8 Typical values for direct-combustion furnaces are 70 to 75 percent; heat loss

principally results from heated stack-gasses

lost during combustion, This definition does

not give a complete measure of the fuel required to heat a living space over the heating season. A more useful definition which

accounts for this, and which is increasingly

being used, is the seasonal performance factor or seasonal efficiency. This measure

compares performances of various spaceheating systems. It is defined as the ratio of

the amount of useful heat delivered to the

home to the heating content of the fuel the

furnace used over the entire heating season.

Typical gas furnaces have seasonal efficiencies in the range of 45 to 65 percent (figure

Xl 1-8). Seasonal efficiency accounts for all

factors affecting the heating system’s performance in its actual operating environ7Conley, General Electr

municatlon, 1977

‘Hlse and Holman, op clt

c Corp , private com-
Ch. XII Heating and Cooling Equipment ● 515

I

cd oJ -

1-

1-

0

1

7
516 ● Solar Technology to Today’s Energy Needs

Figure XII-8. – Residential Heating Systems

OIL

Steady-State Efficiency

(3) Columbus, Ohio

(1) New England

(2) New York

(4) Washington, D.C.

(8) U.S.

Seasonal Efficiency

(4) Washington, D. C.

(4) Maryland

(5) New York

(6) U.S.

(7) Us.

(8) Us.

(9) Us.

(10) Philadelphia

GAS

Steady-State Efficiency

(3) Long Island

Seasonal Efficiency

(14) Baltimore

(12) Canton, Ohio

(10) Philadelphia

(13) Philadelphia

(4) Washington., D.C.

(429—well maintaine

(72—as found)

mversion)

v

o 20% 40% 60% 80% 100%

SOURCE: J. H. Leggoa, “Seasonal Efflclency of Home Fuel 011 Furnaces”

Phdadeiphla Electric Company PapeC Aug. 26, 1976.

ment. In addition to stack gas losses (the

largest contributor) these factors include

loss of heated room air through the chimney

while the furnace is off, cycling losses, pilot

light (gas furnaces only), and heat losses

through the air distribution ducts when in

unheated spaces.9 Cycling losses are a result

of operation at part loads, which causes

heat to be lost in raising the temperature of

the furnace before useful heat can be

delivered to the living space. A recent

measurement of this part-load performance

‘G Samuels, et al , MIUS Systems Ana/ysis– /rtitia/

Comparisons of Modular-Sized Integrated Utility Systems and Convention/ Systems, ORNL/H UD/Ml US-6,

June 1976, p 24.

is indicated in figure Xl 1-9. The seasonal efficiency of many installations is reduced

Figure Xll-9.— Efficiency of Gas Furnaces

80

60

40

20

Oak Rtdge’

t

20 40 60 80 100

by
Ch. XII Heating and Cooling Equipment 517

installing units which are larger than necessary, meaning that the systems are always

operating at relatively inefficient part-load

conditions. 10

In addition to the fossil fuel required for

the burner, gas and oil furnaces and boilers

require electric energy to operate fans and

pumps. A typical small gas furnace will require about 13 watts per 1,000 Btu/hour

capacity, 11 A large central boiler and hotwater distribution system wiII also require

about 13 watts per 1,000 Btu/hour of heating

capacity to pump heated water. 2

Potential for Improving Performance

The performance of gas furnaces can be

increased by improving fan controls, using

systems which preheat the air entering the

furnace with the heat in the chimney, installing an electric ignition system to replace the

pilot, and a variety of other rather straightforward changes in design, A recent study

conducted by the Oak Ridge National Laboratory estimated that fuIl-load combustion

efficiencies of gas furnaces could be increased from 75 to 82 percent if these

changes were implemented. 13 The combustion efficiency of oil-burning furnaces can

also be improved by using improved burner

heads and by ensuring that the burners are

welI maintained

An entirely different approach to the

problem, using fossil fuels to operate a heat

pump, has been under investigation for

some time under the sponsorship of the

American Gas Association. These designs

burn fuel to operate a small onsite heat

engine, which in turn drives the heat-pump

compressor.

An advanced fossil fuel heating concept

involves using the fuel to power a small heat

engine directly coupled to the compressor

‘“H Ise and Hol man, op clt

‘ ‘Sears Fall-W Inter Catalog, 1976, p 955

‘‘1 bld

‘ ‘Hlse and Holman, op cit , p 3

or a heat pump (figure Xl l-l O). The heat rejected by this engine can be used to maintain a source of heated water, which can

then provide the heat pump with a source of

thermal energy at a temperature higher than

the ambient air. Studies of this approach

Figure XII-10.—A Fossil-Fired Heat-Pump System

Hot Alr

T O Builldlnq

r

Heat Pump

Outdoor

Compressor

Heat

Exchanger

1 %

I

I

I

Heat

Engine

SOURCE OT A

have been underway for some time in industrial laboratories and a number of projects in this area have been supported by the

American Gas Association.

A variety of different heat-engine designs

have been considered. Designs employing

Stirling and Ericsson cycles are being examined by RCA, the N.V. Philips Corporation,

Sun Power, Inc., Energy Research and Generation, Inc., and by the University of

Washington .

14 15 16 A number of working

systems have been designed and tested.

“W Beale (Sun Power, Inc.), private communication, June 1976

“G Benson (Energy Research and Generation, Inc ),

Therrna/ Osci//ations, presented at 8th I ECEC meeting,

Aug 14, 1973

‘‘W R Martlnl, Developments in Stirling Engines,

presented to the Annual Winter Meeting of the American Society of Mechanical E nglneers, New York, N.Y ,

Nov 26-30, 1972
518 Solar Technology to Today’s Energy Needs

A number of advanced, gas-fired, heatpump systems are being examined by the industry, with the support of DOE and the

American Gas Association:* **

●

●

●

●

The

the

An absorption system capable of producing both heating and cooling is

being developed by the Allied Chemical

Corporation and the Phillips Engineering Co.

A concept which uses a subatmospheric

gas turbine is being developed by the

Garrett Air Research Corporation.

A free-piston Stirling engine is being

developed by the General Electric Corporation (the project received about $1

miIIion from the American Gas Association and about $2 million from DOE in

1 977).

Systems based on diesel engines and

Rankine-cycle devices are also being examined.

technology of the engines used to drive

compressors was discussed in greater

detail in the previous chapter. An interesting

feature of the heat-fired, heat-pump systems

is that their performance does not decrease

with temperature as fast as the performance

of conventional heat pumps.

While working systems have been designed, commercial production is unlikely to

begin for the next 5 to 10 years.

The performance of the engines being

considered for use with fossil-fired heat

pumps is discussed in greater detail in the

section on Solar Heat Engines in this chapter.

Stirling and Ericsson cycle, free-piston

devices may be able to achieve efficiencies

in the order of 60 to 90 percent of ideal Carnot efficiency. 17 An engine operating be-

*“Advanced Gas-Fired Heat Pumps Seen Cutting

Heating E3111s in Half, ” Energy Users Report #188, Mar

17, 1977, p 25

* * Paul F Swenson, “Competltlon Coming In Heat

Pumps Gas-Fired May Be Best In Cold Climate, ”

Energy Research Reports, Vol 3, No 5, Mar 7, 1977,

p 2

‘ ‘Benson, 011 clt

tween 1,4000 and 1000 F could therefore

achieve a cycle efficiency of 40 to 63 percent. (ERG has reported a measured indicated efficiency which represents 90 percent of Carnot in a free-piston device

operating i n roughly this temperature region. )18 The Garrett Corporation has

reportedly achieved a cycle efficiency of 38

percent, using a small regenerated gas turbine .

If it is assumed that seasonal performance

factors for heat pumps can be in the range

of 2.5 to 3.0, the overalI system COP (or ratio

of heat energy delivered to the Iiving space

to the heating value of the fuel consumed)

of a heat pump combined with a heat engine

which is 38 to 60 percent efficient can be in

the range of 0.95 to 1.8, If waste heat from

the engine is used, the effective COP can be

as high as 2.2.

A 38- to 60-percent efficient engine combined with an air-conditioning cycle with a

COP of 2.5 could achieve system COPS of

0.95 to 1.5. These coefficients cannot be

compared directly with COPS of electric

heat pumps. In order to obtain comparable

“system efficiency” for an electric system,

the electric COPS must be reduced by the efficiency of converting primary fuels to electricity and transmitting this energy to a heatpump system. The average generating efficiency in U.S. utilities is approximately 29

percent, the average transmission losses, approximately 9 percent. Under these assumptions, an electric heat pump with a heating

COP of 3.0 and a cooling COP of 2.5 would

have an effective “system” COP of 0.79 for

heating and 0.66 for cooling. There are a

number of questions about the system’s

performance as an integrated unit, its

reliability, safety, noise, ease of maintenance, etc., which can only be resolved after

much more experience has been obtained.

“lbld

“Patrick G Stone (Garrett Corporation), private

communication, December 1976.
Ch. XII Heating and Cooling Equipment 519

The devices do offer the prospect of a much

more efficient approach to converting fossiI

fuels to useful space-conditioning,

A major question concerning any onsite

system requiring oil or gas is whether these

fuels will continue to be available at acceptable prices, or whether they wilI be available

at al 1. The heat-engine devices just discussed

could, at least in principle, be used in connection with a coal-burning, fluidized-bed

boiler or other system, and thus might present a promising long-term alternative. One

advantage of electric systems is that they

may be able to use a greater variety of

primary fuels than onsite systems.

ABSORPTION AIR= CONDITIONING

An “absorption-cycle” device for using

direct thermal energy to operate air-conditioning systems has been available f o r

some time. A standard cycle is illustrated in

figure Xl 1-11. The refrigeration cycle is very

similar to cycles used in other types of airconditioning systems (vapor-compression). A

chilled liquid (usually water instead of a

refrigerant) is permitted to expand and cool

air. This water is then recompressed and the

Figure XII-11 .—Basic Single-Effect Absorption

Refrigeration Cycle -

1

Refrigerant

(Liquid) I

Heat I I Heat Input

Reject!on (Coollng Load)

SOURCE: National Science Foundation.

absorbed heat rejected into the atmosphere

(this cycle is on the right side of figure

Xl 1-11). The absorption cycle accomplishes

this recompression by absorbing the lowpressure water vapor in a concentrated salt

solution. This concentrated solution is continuously produced in a distilling unit which

is driven by the heat from the fuel.

The cooling performed by the absorption

system can be separated into two distinct

phases, and it would therefore be possible to

store the concentrated salt solution for use

when required by the cooling load. This concept is discussed further in chapter Xl,

Energy Storage. The major limitation to such

a procedure at present is the cost of the

working fIuids,

An enormous amount of time and money

has been invested in the search for better

working fluids. Lithium bromide/water solutions are used most frequently at present.

Ammonia/water solutions are also used.

Absorption units are inherently more expensive than electric systems 1 ) because of

the larger number of heat exchangers required, and 2) because the unit’s cooling

towers must be large enough to reject both

heat from the combustion process and heat

removed from the space which was cooled.

(In electric systems, the heat from generation is rejected at the electric generator

site )

Double-effect units are also more expensive than single-effect devices because even

smaIIer numbers are produced An anaIysis
520 Solar Technology to Today’s Energy Needs

of the components required indicates that

double-effect machines could cost about 20

percent more than single-effect units in the

same capacity range. The prices shown in

figure X I I-1 2 indicate that double-effect

units operating at 3050 F instead of 3600 F

would cost nearly twice as much because

capacity would be decreased. Little work

has been done to produce an optimum design for low-temperature systems, and D O E

is currently funding several projects in this

area.

The only small absorption units now on

the market are the Arkla single-effect devices, manufactured in 3- and 25-ton sizes.

There are currently no small double-effect

machines on the market. In the early 1960’s,

the Iron Fireman Webster Division of the

Electronic Specialties Corporation briefly

700

600

500

400

$/Ton

300

200

100

marketed a small (1 5-ton) Iithium bromide,

double-effect, absorption machine. The design was taken from work supported in part

by the American Gas Association, and was

apparently capable of achieving very high

efficiencies. It was removed from th e

market after only a few hundred were sold,

apparently because the company felt that it

could not overcome problems with the system’s reliability at a reasonable cost. The

unit was sufficiently different from singleeffect units that gas company maintenance

personnel had difficulty repairing the devices. The unit at least demonstrated the

feasibility of small double-effect units.

System Performance

The coefficient of performance (COP) of

contemporary absorption air-conditioners is

Figure Xll-12.— Estimated Refrigeration Unit Cost Per Ton, 12,000 Btu/hr(contractor’s cost)*

I I I I I 1 I I I

1. Single Effect Absorption, 195° F Supply Water

2. Single Effect Absorption, 250° F Supply Water

3. Double Effect Absorption, 305° F Supply Water

4. Double Effect Absorption, 360° F Supply Water

5. Electro-Mechanical Vapor Compression–Reciprocating

6. Electro-Mechanical Vapor Compression-Centrifugal

L

o 40 80 120 160 200 240 280 320 380 400

Unit Size in Tons

.Industry Average- 1976 Costs

NOTE Prices do not Include Inslallat!on or subcontractor O&P costs

SOURCE prepared for OTA by H CorbY r) Rooks April 1976
Ch. XII Heating and Cooling Equipment 521

shown in figure Xl 1-13. A typical singleeffect device has a COP of 0.65 and doubleeffect units can have COPS of 1.1. These

COPS must, however, be carefully qualified.

(As in the case of fossil-fired heat pumps,

these COPS should be compared with the

“system” COPs of electric system s.)

The COPS shown in figure Xl 1-13 include

neither the electric energy required to operate pumps which move chilled water to the

building loads and cooling water to and

from the cooling tower, nor the electricity

required to operate the fan in the cooling

tower. These ancillary units require about

0.14 kW per ton of cooling in a typical instalIation. 20

20 Samuels, et al , op cit , p 20

1.2

1.1

1.0

.9

.8

.7

COP

.6

.5

.4

.3

.2

.1

0

With-85 0 Cooling Tower Water to Unit

44° Chilled Water Temp. From Unit

The COPS also do not include the inefficiency of the boiler which must be used

when the absorption units are used with

fossil fuels. Typical boilers used in such applications lose about 20 to 22 percent of the

heating value of the fuel burned in hot

gasses escaping up the chimney. The COPS

shown in the figure would apply to units

operated from solar-heated fluids or by

steam generated by a waste-heat boilerconnected to a direct or other heat engine. They

must be reduced by 20 to 22 percent when

used to represent the performance of directfired devices.

It is reasonable to expect that improvements in current designs could lead to significant improvements in performance. A

new series of absorption units, soon to be

marketed by Arkla, will probably achieve a

COP greater than 0.7 for a single-effect deI I

100 140

I I I I /

.

‘.

I I I 1 I I I I I A

180 220 260 300 340 380 420 440

Temperature of the Supply Water (“F)

SOURCE Prepared for OTA by H Corbyn Rooks, April 1976
522 ● Solar Technology to Today’s Energy Needs

vice with no substantial increase in price. An

experimental machine, which was a modified version of the single-effect Arkla device, has been tested with a COP greater

than 0.8. 21

The Iron-Firemen double-effect device

discussed previously was able to achieve a

COP of 1.2 (not including boiler losses and

electric energy requirements) .22 Some engineers believe that it would be possible to

CONVENTIONAL

WATER

Residential hot water heaters are very inefficient. z

’ A gas water heater has a COP of

about 0.50, and an electric water heater a

COP of about 0.75. 25 2 ’ 27 Better insulation

and other improvements could increase the

COPS of future electric units to 0.85 and the

construct double-effect absorption devices

with COPS in the range of 1.35.23

Absorption units have good performance

at partial loads because their effective

capacity can be varied by simply changing

the rate at which the salt solutions are

pumped through the systems. This type of

control works until the load falIs to about 35

percent of the peak load, at which point

substantial inefficiencies are experienced.

GAS AND ELECTRIC

HEATERS

COPS of gas units to 0.80.

The efficiency of water heaters varies

somewhat as a function of loads, but for

simplicity it is assumed that water heaters

have a constant “average” efficiency.

OPERATING COSTS

The costs of operating conventional heating and cooling equipment (exclusive of fuel

costs) are not well documented, and no extensive study has been conducted on the

subject. The estimates used in later analyses

are shown in tables Xl I-3 and Xl 1-4. The costs

used in this study were taken from the costs

of purchasing a service and maintenance

contract for equipment installed in the

Washington, D. C., area. The actual costs will

vary as a function of geographic location,

quality of the equipment, location of the

equipment in the building, design of the

systems, etc. The costs must be considered

conservative since the selIers of mainte2’joseph Murray, Chief Engineer of Applied Systems, Airtemp Corporation, private communication,

Sept 23,1976

‘Z)oseph Murray, private communication, 1977

2’G.C Vllet, et al , A Thermodynamic Approach to

the Developments of a More Efficient Absorption AirConditioning System, University of Texas at Austin –

Center for Energy Studies

nance contracts must increase the actual

maintenance costs by a margin sufficient to

cover overhead and profit requirements.

Table XII-3. — Average Cost of Maintenance

Contracts for Residential Heating

and Cooling Equipment

——. . . —

Annual

cost

Gas furnace and eleotric air-conditioning $60

Air-to-air heat pump $50

Baseboard electric heat and window

air-oonditioners $30

—— ————.... . —

SOURCE Gordlan Associates, Inc Evaluation of the Air-to-Air Heat Pump for

Resldentlal Space-Condltlonmg. April 1976

24 CiIlman, op clt

2’APS, Efficient Use of Energy, p 83.

“J J. Mutch, Residential Water Heating, Fue/ Conservation Economics and Public Policy, pp. 8 and 55

27 Arthur D Little Co,, Study of Energy-Savings Options for Refrigerators and Water Heaters, draft, pp

S-12,1 3,14
Ch. XII Heating and Cooling Equipment ● 5 2 3

Table XII-4. —Cost of Maintaining Commercial

Heating and Cooling Equipment*

(Parts and Labor)

Low Rise

Heating (106 Btu/hour)

Gas . . . . . . . . . . . . . . . . . . . . . . $1,000 $1,000

Oil . . . . . . . . . . . . . . . . . . . . ..... 1,250 1,250

Electric . . . . . . . . . . . . . . . . . . . . .1,000 1,000

Cooing (50 tons)

Gas. ... ... ..... .... ........ 3,8OO-4,5OO 6,300-7,500

Electric ..... .... ........ ....3,000-3,6OO 5,000-6,000

High Rise

Heating (2 units@ 2x106

Btu/hour)

Gas . . . . . . . . . . . . . . . . . . . . . . . . 2,000

oil . . . . . . . . . . . . . . . . . . . . . . . . . 2,500 625

Electric . ....................2,000

Cooling(200tons)

Gas . .......................5,000-6,000 2,000-2,500

Electric...............................4,000-5,000 1,700-2,000

Shopping Center

Heating (2 units@ 8x106

Btu/hour)

Gas . .......................2,500 150

Oil . . . . . . . . . . . . . . . . . . . . . ... .3,000 190

Electric . ....................2,500 150

Cooling(2000tons)

Gas. . . . . . . . . . . . . .........19,000 800

Electric . .................15,000 600

‘Actual costs wIfl vary greatly as a function of equipment quality, lnstallatron, bulldlng features, etc Costs based on “very rough’

estimates of Robert NoYes of R E Donovan Co, Inc a service corn.

pany[nthe Wasthlngton DC area Sept 23 1976

ADAPTATION OF CONVENTIONAL

TO SOLAR POWER

Conventional heating and cooling equipment can be integrated with solar energy in

two basic ways: 1 ) electricity or mechanical

energy generated by solar energy devices

can be used to supplement electricity purchased from a utility, and 2) direct use of

thermal energy generated by solar devices

can provide a

EQUIPMENT

source of thermal energy for

liquid and air-heat pumps, for absorption

air-conditioning, forced-air heating, and to

heat domestic hot water.

The direct use of solar-heated fluids for

space heating or for the heating of hot water
524 ● Solar Technology to Today’s Energy Needs

requires no sophisticated equipment, and

the problems of designing these systems are

discussed elsewhere.

SOLAR HEAT ENGINES

Direct use of solar-heated fIuids can operate heat engines such as Rankine cycle turbines or Stirling engine devices which are

coupled mechanically to heat pumps and

air-conditioners. The direct-drive systems

have a substantial theoretical advantage

over systems operating from solar-generated

electricity in that the losses associated with

a motor and generator can be avoided. This

can be a substantial gain, since typical efficiencies of small motors and generators are

in the range of 80 to 90 percent and combined losses can amount to 30 percent.

Total energy systems, which use the solarpowered engine to drive both a generator

and a heat pump, could be driven directly

from utility electricity when solar energy is

not available by using the electric generator

as a motor to drive the compressor. Directdrive systems have a potential disadvantage

if they cannot be designed as a single-sealed

unit, since seals on rotating shafts could

reduce overall system reliability. It may be

possible to develop completely sealed engine-compressor units, but this wilI require a

lengthy development program,

All of the heat engine alternatives are discussed in detail in the chapter discussing the

conversion of solar energy into electricity.

The operating characteristics of conventional heat pumps and air-conditioners integrated into solar energy designs using

direct-drive connections will need adjustment to eliminate the inefficiency of the

motors used in conventional systems. F or

the purposes of the calculations whic h

follow, it is assumed that the motors used on

conventional systems are 80 percent efficient. Systems connected electrically are

assumed to be identical to conventional

equipment, and conventional performance

characteristics are assumed.

SOLAR ABSORPTION EQUIPMENT

Absorption cooling equipment can be

easily converted for use with solar-heated

fluids, and the modifications being suggested for high-performance solar applications should not require major design

changes. As a result, absorption equipment

will probably represent the majority of units

used in solar air-conditioning systems in the

near future. The water sent to the absorption generator can be heated either from a

conventional boiler or from a solar collector. The coefficients of performance used

for solar absorption equipment will be the

same as those used for the steam-driven absorption equipment, since no boiler losses

are involved.

The Adsorption Cycle System

The adsorption cycle was originally

developed by Carl Munters of Stockholm,

and is often known as the Munters system.

The system is basically a desiccant system,

drying the air with various kinds of salt

crystals, silica gels, or zeolite. Heat and

moisture are typically exchanged between

an exhaust airstream and a supply airstream

using a heat exchange wheel and a drying

wheel as shown in figure Xl 1-14. The air is

taken from the room and passed over the

drying wheel which contains the desiccant.

In passing through this wheel, the air is dried

and heated to about 180 o

F. It then passes

through the heat exchange wheel, where it

cools to near room temperature. The air is

finally passed through a humidifier, where it

picks up moisture and cools to 550 to 600 F.

The exhaust airstream takes ambient air and

humidifies and cools it slightly to keep the

heat exchange wheel as cool as possible.

After passing through the heat exchange

wheel, the air is still not hot enough to drive

the moisture out of the drying wheel, so additional heat from a solar or gas source is

added. This hot air then passes through the

drying wheel, where it evaporates moisture

from the desiccant, and the moist, heated

air is exhausted to the atmosphere,
Ch. XII Heating and Cooling Equipment ● 525

Its advantage is that it takes no refrigeration unit, but the wheels are large and require power to drive. After years of development, problems still exist with desiccant

systems, including the desiccant, the seals

between the supply and discharge airstream

Ambient

Humidifiers \ \

on the rotating wheels, and the wet pads.

Variations of this adsorbent system are being properly supported by DOE. It has advantages, but still requires development

prior to demonstration.

Figure XII-14. —An Adsorption Chiller

Heat Gas Burner

Exchange or Solar Heat

Wheel I

56.5o/53o

SOURCE Based on a drawtng by W F Rush, statement relative to H R 10952

(Institute of Gas Technology, Illlnols Institute of Technology, Chicago, Ill ) Nov 14, 1973